diff --git a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNS.java b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNS.java
index 89af08f5..3879a65f 100644
--- a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNS.java
+++ b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNS.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, Harald Kuhr
+ * Copyright (c) 2017, Harald Kuhr
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -92,14 +92,28 @@ interface ICNS {
     /** 128×128 8-bit mask. */
     int t8mk = ('t' << 24) + ('8' << 16) + ('m' << 8) + 'k';
 
-    /** 256×256 JPEG 2000 or PNG icon (10.x+). */
+    /** 16x16 JPEG2000 or PNG icon (10.7+). */
+    int icp4 = ('i' << 24) + ('c' << 16) + ('p' << 8) + '4';
+    /** 32x32 JPEG2000 or PNG icon (10.7+). */
+    int icp5 = ('i' << 24) + ('c' << 16) + ('p' << 8) + '5';
+    /** 64x64 JPEG2000 or PNG icon (10.7+). */
+    int icp6 = ('i' << 24) + ('c' << 16) + ('p' << 8) + '6';
+    /** 128x128 JPEG2000 or PNG icon (10.7+). */
+    int ic07 = ('i' << 24) + ('c' << 16) + ('0' << 8) + '7';
+    /** 256×256 JPEG 2000 or PNG icon (10.5+). */
     int ic08 = ('i' << 24) + ('c' << 16) + ('0' << 8) + '8';
-
-    /** 512×512 JPEG 2000 or PNG icon (10.x+). */
+    /** 512×512 JPEG 2000 or PNG icon (10.5+). */
     int ic09 = ('i' << 24) + ('c' << 16) + ('0' << 8) + '9';
-
-    /** 1024×1024 PNG icon (10.7+). */
+    /** 1024×1024 JPEG2000 or PNG icon (10.7+) OR 512x512@2x "retina" (10.8+). */
     int ic10 = ('i' << 24) + ('c' << 16) + ('1' << 8) + '0';
+    /** 16x16@2x "retina" JPEG2000 or PNG icon (10.8+). */
+    int ic11 = ('i' << 24) + ('c' << 16) + ('1' << 8) + '1';
+    /** 32x32@2x "retina" JPEG2000 or PNG icon (10.8+). */
+    int ic12 = ('i' << 24) + ('c' << 16) + ('1' << 8) + '2';
+    /** 128x128@2x "retina" JPEG2000 or PNG icon (10.8+). */
+    int ic13 = ('i' << 24) + ('c' << 16) + ('1' << 8) + '3';
+    /** 256x256@2x "retina" JPEG2000 or PNG icon (10.8+). */
+    int ic14 = ('i' << 24) + ('c' << 16) + ('1' << 8) + '4';
 
     /** Unknown (Version). */
     int icnV = ('i' << 24) + ('c' << 16) + ('n' << 8) + 'V';
diff --git a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageReader.java b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageReader.java
index a4476dc5..82962c98 100644
--- a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageReader.java
+++ b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageReader.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, Harald Kuhr
+ * Copyright (c) 2017, Harald Kuhr
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -31,6 +31,7 @@
 package com.twelvemonkeys.imageio.plugins.icns;
 
 import com.twelvemonkeys.imageio.ImageReaderBase;
+import com.twelvemonkeys.imageio.stream.SubImageInputStream;
 import com.twelvemonkeys.imageio.util.IIOUtil;
 import com.twelvemonkeys.imageio.util.ImageTypeSpecifiers;
 
@@ -422,7 +423,7 @@ public final class ICNSImageReader extends ImageReaderBase {
 
     private BufferedImage readForeignFormat(int imageIndex, final ImageReadParam param, final IconResource resource) throws IOException {
         // TODO: Optimize by caching readers that work?
-        ImageInputStream stream = ImageIO.createImageInputStream(IIOUtil.createStreamAdapter(imageInput, resource.length));
+        ImageInputStream stream = new SubImageInputStream(imageInput, resource.length);
 
         try {
             // Try first using ImageIO
@@ -441,7 +442,7 @@ public final class ICNSImageReader extends ImageReaderBase {
                     }
                     else {
                         stream.close();
-                        stream = ImageIO.createImageInputStream(IIOUtil.createStreamAdapter(imageInput, resource.length));
+                        stream = new SubImageInputStream(imageInput, resource.length);
                     }
                 }
                 finally {
@@ -524,10 +525,28 @@ public final class ICNSImageReader extends ImageReaderBase {
         }
 
         IconResource resource = IconResource.read(imageInput);
-//        System.err.println("resource: " + resource);
+
+        if (resource.isTOC()) {
+            // TODO: IconResource.readTOC()?
+            int resourceCount = (resource.length - ICNS.RESOURCE_HEADER_SIZE) / ICNS.RESOURCE_HEADER_SIZE;
+            long pos = resource.start + resource.length;
+
+            for (int i = 0; i < resourceCount; i++) {
+                resource = IconResource.read(pos, imageInput);
+                pos += resource.length;
+                addResource(resource);
+            }
+        }
+        else {
+            addResource(resource);
+        }
 
         lastResourceRead = resource;
 
+        return resource;
+    }
+
+    private void addResource(final IconResource resource) {
         // Filter out special cases like 'icnV' or 'TOC ' resources
         if (resource.isMaskType()) {
             masks.add(resource);
@@ -535,8 +554,6 @@ public final class ICNSImageReader extends ImageReaderBase {
         else if (!resource.isUnknownType()) {
             icons.add(resource);
         }
-
-        return resource;
     }
 
     private void readeFileHeader() throws IOException {
diff --git a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriter.java b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriter.java
new file mode 100644
index 00000000..56641a40
--- /dev/null
+++ b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriter.java
@@ -0,0 +1,273 @@
+/*
+ * Copyright (c) 2017, Harald Kuhr
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ * * Neither the name of the copyright holder nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.twelvemonkeys.imageio.plugins.icns;
+
+import com.twelvemonkeys.imageio.ImageWriterBase;
+import com.twelvemonkeys.imageio.stream.SubImageOutputStream;
+import com.twelvemonkeys.imageio.util.ProgressListenerBase;
+
+import javax.imageio.*;
+import javax.imageio.event.IIOWriteWarningListener;
+import javax.imageio.metadata.IIOMetadata;
+import javax.imageio.spi.ImageWriterSpi;
+import javax.imageio.stream.ImageInputStream;
+import javax.imageio.stream.ImageOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.util.Iterator;
+
+/**
+ * ICNSImageWriter
+ */
+public final class ICNSImageWriter extends ImageWriterBase {
+
+    private int sequenceIndex = -1;
+    private ImageWriter pngDelegate;
+
+    ICNSImageWriter(ImageWriterSpi provider) {
+        super(provider);
+    }
+
+    @Override
+    protected void resetMembers() {
+        sequenceIndex = -1;
+
+        if (pngDelegate != null) {
+            pngDelegate.dispose();
+            pngDelegate = null;
+        }
+    }
+
+    @Override
+    public IIOMetadata getDefaultImageMetadata(final ImageTypeSpecifier imageType, final ImageWriteParam param) {
+        return null;
+    }
+
+    @Override
+    public IIOMetadata convertImageMetadata(final IIOMetadata inData, final ImageTypeSpecifier imageType, final ImageWriteParam param) {
+        return null;
+    }
+
+    @Override
+    public void write(final IIOMetadata streamMetadata, final IIOImage image, final ImageWriteParam param) throws IOException {
+        prepareWriteSequence(streamMetadata);
+        writeToSequence(image, param);
+        endWriteSequence();
+    }
+
+    @Override
+    public boolean canWriteSequence() {
+        return true;
+    }
+
+    @Override
+    public void prepareWriteSequence(final IIOMetadata streamMetadata) throws IOException {
+        assertOutput();
+
+        // TODO: Allow TOC resource to be passed as stream metadata?
+        // - We only need number of icons to be written later
+        // - The contents of the TOC could be updated while adding to the sequence
+
+        if (sequenceIndex >= 0) {
+            throw new IllegalStateException("writeSequence already started");
+        }
+
+        writeICNSHeader();
+        sequenceIndex = 0;
+    }
+
+    @Override
+    public void endWriteSequence() throws IOException {
+        assertOutput();
+
+        if (sequenceIndex < 0) {
+            throw new IllegalStateException("prepareWriteSequence not called");
+        }
+
+        // TODO: Now that we know the number of icon resources, we could move all data backwards
+        // and write a TOC... But I don't think the benefit will outweigh the cost.
+
+        sequenceIndex = -1;
+    }
+
+    @Override
+    public void writeToSequence(final IIOImage image, final ImageWriteParam param) throws IOException {
+        assertOutput();
+
+        if (sequenceIndex < 0) {
+            throw new IllegalStateException("prepareWriteSequence not called");
+        }
+
+        if (image.hasRaster()) {
+            throw new UnsupportedOperationException("image has a Raster");
+        }
+
+        long resourceStart = imageOutput.getStreamPosition();
+
+        // TODO: Allow for other formats based on param?
+        // - Uncompressed/RLE (only allowed up to 128x128)?
+        // - JPEG2000 not very likely...
+
+        // Validate icon size, get icon resource type based on size and compression
+        // TODO: Allow smaller, centered in larger square? Resize?
+        imageOutput.writeInt(IconResource.typeFromImage(image.getRenderedImage(), "PNG"));
+        imageOutput.writeInt(0); // Size, update later
+
+        processImageStarted(sequenceIndex);
+
+        // Write icon in PNG format
+        ImageWriter writer = getPNGDelegate();
+        writer.setOutput(new SubImageOutputStream(imageOutput));
+        writer.write(null, image, copyParam(param, writer));
+
+        processImageComplete();
+
+        long resourceEnd = imageOutput.getStreamPosition();
+        if (resourceEnd > Integer.MAX_VALUE) {
+            throw new IIOException("File too large for ICNS");
+        }
+
+        int length = (int) (resourceEnd - resourceStart);
+
+        // Update file length field
+        imageOutput.seek(4);
+        imageOutput.writeInt((int) resourceEnd);
+
+        // Update resource length field
+        imageOutput.seek(resourceStart + 4);
+        imageOutput.writeInt((length));
+
+        // Prepare for next iteration
+        imageOutput.seek(resourceEnd);
+    }
+
+    private ImageWriteParam copyParam(final ImageWriteParam param, ImageWriter writer) {
+        if (param == null) {
+            return null;
+        }
+
+        ImageWriteParam writeParam = writer.getDefaultWriteParam();
+        writeParam.setSourceSubsampling(param.getSourceXSubsampling(), param.getSourceYSubsampling(), param.getSubsamplingXOffset(), param.getSubsamplingYOffset());
+        writeParam.setSourceRegion(param.getSourceRegion());
+        writeParam.setSourceBands(param.getSourceBands());
+
+        return writeParam;
+    }
+
+    private ImageWriter getPNGDelegate() {
+        if (pngDelegate == null) {
+            // There's always a PNG writer...
+            pngDelegate = ImageIO.getImageWritersByFormatName("PNG").next();
+            pngDelegate.setLocale(getLocale());
+            pngDelegate.addIIOWriteProgressListener(new ProgressListenerBase() {
+                @Override
+                public void imageProgress(ImageWriter source, float percentageDone) {
+                    processImageProgress(percentageDone);
+                }
+
+                @Override
+                public void writeAborted(ImageWriter source) {
+                    processWriteAborted();
+                }
+            });
+            pngDelegate.addIIOWriteWarningListener(new IIOWriteWarningListener() {
+                @Override
+                public void warningOccurred(ImageWriter source, int imageIndex, String warning) {
+                    processWarningOccurred(sequenceIndex, warning);
+                }
+            });
+        }
+
+        return pngDelegate;
+    }
+
+    private void writeICNSHeader() throws IOException {
+        if (imageOutput.getStreamPosition() != 0) {
+            throw new IllegalStateException("Stream already written to");
+        }
+
+        imageOutput.writeInt(ICNS.MAGIC);
+        imageOutput.writeInt(8); // Length of file, in bytes, must be updated while writing
+    }
+
+    public static void main(String[] args) throws IOException {
+        boolean pngCompression = false;
+        int firstArg = 0;
+
+        while (args.length > firstArg && args[firstArg].charAt(0) == '-') {
+            if (args[firstArg].equals("-p") || args[firstArg].equals("--png")) {
+                pngCompression = true;
+            }
+
+            firstArg++;
+        }
+
+        if (args.length - firstArg < 2) {
+            System.err.println("Usage: command [-p|--png] <output.ico> <input> [<input>...]");
+            System.exit(1);
+        }
+
+        try (ImageOutputStream out = ImageIO.createImageOutputStream(new File(args[firstArg++]))) {
+            ImageWriter writer = new ICNSImageWriter(null);
+            writer.setOutput(out);
+
+            ImageWriteParam param = writer.getDefaultWriteParam();
+            // For now, we only support PNG...
+//            param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
+//            param.setCompressionType(pngCompression ? "BI_PNG" : "BI_RGB");
+
+            writer.prepareWriteSequence(null);
+
+            for (int i = firstArg; i < args.length; i++) {
+                File inFile = new File(args[i]);
+                try (ImageInputStream input = ImageIO.createImageInputStream(inFile)) {
+                    Iterator<ImageReader> readers = ImageIO.getImageReaders(input);
+
+                    if (!readers.hasNext()) {
+                        System.err.printf("Can't read %s\n", inFile.getAbsolutePath());
+                    }
+                    else {
+                        ImageReader reader = readers.next();
+                        reader.setInput(input);
+                        for (int j = 0; j < reader.getNumImages(true); j++) {
+                            IIOImage image = reader.readAll(j, null);
+                            writer.writeToSequence(image, param);
+                        }
+                    }
+                }
+            }
+
+            writer.endWriteSequence();
+            writer.dispose();
+        }
+    }
+
+}
diff --git a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriterSpi.java b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriterSpi.java
new file mode 100644
index 00000000..bf207e39
--- /dev/null
+++ b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriterSpi.java
@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2017, Harald Kuhr
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ * * Neither the name of the copyright holder nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.twelvemonkeys.imageio.plugins.icns;
+
+import com.twelvemonkeys.imageio.spi.ImageWriterSpiBase;
+
+import javax.imageio.ImageTypeSpecifier;
+import java.util.Locale;
+
+/**
+ * ICNSImageWriterSpi
+ */
+public final class ICNSImageWriterSpi extends ImageWriterSpiBase {
+    public ICNSImageWriterSpi() {
+        super(new ICNSProviderInfo());
+    }
+
+    @Override
+    public boolean canEncodeImage(final ImageTypeSpecifier type) {
+        return true;
+    }
+
+    @Override
+    public ICNSImageWriter createWriterInstance(final Object extension) {
+        return new ICNSImageWriter(this);
+    }
+
+    @Override
+    public String getDescription(final Locale locale) {
+        return "Apple Icon Image (icns) format Writer";
+    }
+}
diff --git a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSProviderInfo.java b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSProviderInfo.java
index 153257ef..9fe2b6a6 100644
--- a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSProviderInfo.java
+++ b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/ICNSProviderInfo.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, Harald Kuhr
+ * Copyright (c) 2017, Harald Kuhr
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -40,7 +40,7 @@ import com.twelvemonkeys.imageio.spi.ReaderWriterProviderInfo;
  * @version $Id: ICNSProviderInfo.java,v 1.0 20/03/15 harald.kuhr Exp$
  */
 final class ICNSProviderInfo extends ReaderWriterProviderInfo {
-    protected ICNSProviderInfo() {
+    ICNSProviderInfo() {
         super(
                 ICNSProviderInfo.class,
                 new String[]{"icns", "ICNS"},
@@ -50,9 +50,12 @@ final class ICNSProviderInfo extends ReaderWriterProviderInfo {
                 },
                 "com.twelvemonkeys.imageio.plugins.icns.ICNSImageReader",
                 new String[] {"com.twelvemonkeys.imageio.plugins.icns.ICNSImageReaderSpi"},
+                "com.twelvemonkeys.imageio.plugins.icns.ICNSImageWriter",
+                new String[] {"com.twelvemonkeys.imageio.plugins.icns.ICNSImageWriterSpi"},
+                false, null, null,
                 null, null,
-                false, null, null, null, null,
-                true, null, null, null, null
+                true, null,
+                null, null, null
         );
     }
 }
diff --git a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/IconResource.java b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/IconResource.java
index bde54b32..d9b111a2 100644
--- a/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/IconResource.java
+++ b/imageio/imageio-icns/src/main/java/com/twelvemonkeys/imageio/plugins/icns/IconResource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, Harald Kuhr
+ * Copyright (c) 2017, Harald Kuhr
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -34,6 +34,7 @@ import com.twelvemonkeys.lang.Validate;
 
 import javax.imageio.stream.ImageInputStream;
 import java.awt.*;
+import java.awt.image.RenderedImage;
 import java.io.IOException;
 
 /**
@@ -46,9 +47,9 @@ import java.io.IOException;
 final class IconResource {
     // TODO: Rewrite using subclasses/instances!
 
-    protected final long start;
-    protected final int type;
-    protected final int length;
+    final long start;
+    final int type;
+    final int length;
 
     private IconResource(long start, int type, int length) {
         validate(type, length);
@@ -58,8 +59,12 @@ final class IconResource {
         this.length = length;
     }
 
-    public static IconResource read(ImageInputStream input) throws IOException {
-        return new IconResource(input.getStreamPosition(), input.readInt(), input.readInt());
+    static IconResource read(final ImageInputStream input) throws IOException {
+        return read(input.getStreamPosition(), input);
+    }
+
+    static IconResource read(final long offset, final ImageInputStream input) throws IOException {
+        return new IconResource(offset, input.readInt(), input.readInt());
     }
 
     private void validate(int type, int length) {
@@ -113,9 +118,17 @@ final class IconResource {
             case ICNS.is32:
             case ICNS.il32:
             case ICNS.it32:
+            case ICNS.icp4:
+            case ICNS.icp5:
+            case ICNS.icp6:
+            case ICNS.ic07:
             case ICNS.ic08:
             case ICNS.ic09:
             case ICNS.ic10:
+            case ICNS.ic11:
+            case ICNS.ic12:
+            case ICNS.ic13:
+            case ICNS.ic14:
                 if (length > ICNS.RESOURCE_HEADER_SIZE) {
                     break;
                 }
@@ -142,7 +155,7 @@ final class IconResource {
         );
     }
 
-    public Dimension size() {
+    Dimension size() {
         switch (type) {
             case ICNS.ICON:
             case ICNS.ICN_:
@@ -156,11 +169,14 @@ final class IconResource {
             case ICNS.ics8:
             case ICNS.is32:
             case ICNS.s8mk:
+            case ICNS.icp4:
                 return new Dimension(16, 16);
             case ICNS.icl4:
             case ICNS.icl8:
             case ICNS.il32:
             case ICNS.l8mk:
+            case ICNS.icp5:
+            case ICNS.ic11:
                 return new Dimension(32, 32);
             case ICNS.ich_:
             case ICNS.ich4:
@@ -168,12 +184,18 @@ final class IconResource {
             case ICNS.ih32:
             case ICNS.h8mk:
                 return new Dimension(48, 48);
+            case ICNS.icp6:
+            case ICNS.ic12:
+                return new Dimension(64, 64);
             case ICNS.it32:
             case ICNS.t8mk:
+            case ICNS.ic07:
                 return new Dimension(128, 128);
             case ICNS.ic08:
+            case ICNS.ic13:
                 return new Dimension(256, 256);
             case ICNS.ic09:
+            case ICNS.ic14:
                 return new Dimension(512, 512);
             case ICNS.ic10:
                 return new Dimension(1024, 1024);
@@ -182,7 +204,7 @@ final class IconResource {
         }
     }
 
-    public int depth() {
+    int depth() {
         switch (type) {
             case ICNS.ICON:
             case ICNS.ICN_:
@@ -208,16 +230,24 @@ final class IconResource {
             case ICNS.il32:
             case ICNS.ih32:
             case ICNS.it32:
+            case ICNS.icp4:
+            case ICNS.icp5:
+            case ICNS.icp6:
+            case ICNS.ic07:
             case ICNS.ic08:
             case ICNS.ic09:
             case ICNS.ic10:
+            case ICNS.ic11:
+            case ICNS.ic12:
+            case ICNS.ic13:
+            case ICNS.ic14:
                 return 32;
             default:
                 throw new IllegalStateException(String.format("Unknown icon type: '%s'", ICNSUtil.intToStr(type)));
         }
     }
 
-    public boolean isUnknownType() {
+    boolean isUnknownType() {
         // Unknown types should simply be skipped when reading
         switch (type) {
             case ICNS.ICON:
@@ -241,16 +271,24 @@ final class IconResource {
             case ICNS.il32:
             case ICNS.ih32:
             case ICNS.it32:
+            case ICNS.icp4:
+            case ICNS.icp5:
+            case ICNS.icp6:
+            case ICNS.ic07:
             case ICNS.ic08:
             case ICNS.ic09:
             case ICNS.ic10:
+            case ICNS.ic11:
+            case ICNS.ic12:
+            case ICNS.ic13:
+            case ICNS.ic14:
                 return false;
         }
 
         return true;
     }
 
-    public boolean hasMask() {
+    boolean hasMask() {
         switch (type) {
             case ICNS.ICN_:
             case ICNS.icm_:
@@ -262,7 +300,7 @@ final class IconResource {
         return false;
     }
 
-    public boolean isMaskType() {
+    boolean isMaskType() {
         switch (type) {
             case ICNS.s8mk:
             case ICNS.l8mk:
@@ -274,7 +312,7 @@ final class IconResource {
         return false;
     }
 
-    public boolean isCompressed() {
+    boolean isCompressed() {
         switch (type) {
             case ICNS.is32:
             case ICNS.il32:
@@ -291,18 +329,30 @@ final class IconResource {
         return false;
     }
 
-    public boolean isForeignFormat() {
+    boolean isForeignFormat() {
         // Recent entries contains full JPEG 2000 or PNG streams
         switch (type) {
+            case ICNS.icp4:
+            case ICNS.icp5:
+            case ICNS.icp6:
+            case ICNS.ic07:
             case ICNS.ic08:
             case ICNS.ic09:
             case ICNS.ic10:
+            case ICNS.ic11:
+            case ICNS.ic12:
+            case ICNS.ic13:
+            case ICNS.ic14:
                 return true;
         }
 
         return false;
     }
 
+    boolean isTOC() {
+        return type == ICNS.TOC_;
+    }
+
     @Override
     public int hashCode() {
         return (int) start ^ type;
@@ -322,4 +372,62 @@ final class IconResource {
     public String toString() {
         return String.format("%s['%s' start: %d, length: %d%s]", getClass().getSimpleName(), ICNSUtil.intToStr(type), start, length, isCompressed() ? " (compressed)" : "");
     }
+
+    static int typeFromImage(final RenderedImage image, final String compression) {
+        int width = image.getWidth();
+        int height = image.getHeight();
+
+        if (width == height) {
+            switch (compression) {
+                case "JPEG2000":
+                case "PNG":
+                    return typeFromWidthForeign(width);
+                case "None":
+                case "RLE":
+                    return typeFromWidthNative(width);
+                default:
+                    throw new IllegalArgumentException("Unsupported compression for ICNS: " + compression);
+            }
+        }
+
+        // Note: Strictly, the format supports an ancient 16x12 size, but I doubt we'll ever support that
+        throw new IllegalArgumentException(String.format("Unsupported dimensions for ICNS, only square icons supported: %dx%d", width, height));
+    }
+    // NOTE: These also needs a mask, if there's an alpha channel
+
+    private static int typeFromWidthNative(final int width) {
+        switch (width) {
+            case 16:
+                return ICNS.is32;
+            case 32:
+                return ICNS.il32;
+            case 48:
+                return ICNS.ih32;
+            case 128:
+                return ICNS.it32;
+            default:
+                throw new IllegalArgumentException(String.format("Unsupported dimensions for ICNS, only 16, 32, 48 and 128 supported: %dx%d", width, width));
+        }
+    }
+
+    private static int typeFromWidthForeign(final int width) {
+        switch (width) {
+            case 16:
+                return ICNS.icp4;
+            case 32:
+                return ICNS.icp5;
+            case 64:
+                return ICNS.icp6;
+            case 128:
+                return ICNS.ic07;
+            case 256:
+                return ICNS.ic08;
+            case 512:
+                return ICNS.ic09;
+            case 1024:
+                return ICNS.ic10;
+            default:
+                throw new IllegalArgumentException(String.format("Unsupported dimensions for ICNS, only multiples of 2 from 16 to 1024 supported: %dx%d", width, width));
+        }
+    }
 }
diff --git a/imageio/imageio-icns/src/main/resources/META-INF/services/javax.imageio.spi.ImageReaderSpi b/imageio/imageio-icns/src/main/resources/META-INF/services/javax.imageio.spi.ImageReaderSpi
index c5bd0d3a..80a16d1d 100644
--- a/imageio/imageio-icns/src/main/resources/META-INF/services/javax.imageio.spi.ImageReaderSpi
+++ b/imageio/imageio-icns/src/main/resources/META-INF/services/javax.imageio.spi.ImageReaderSpi
@@ -1 +1 @@
-com.twelvemonkeys.imageio.plugins.icns.ICNSImageReaderSpi
\ No newline at end of file
+com.twelvemonkeys.imageio.plugins.icns.ICNSImageReaderSpi
diff --git a/imageio/imageio-icns/src/main/resources/META-INF/services/javax.imageio.spi.ImageWriterSpi b/imageio/imageio-icns/src/main/resources/META-INF/services/javax.imageio.spi.ImageWriterSpi
new file mode 100644
index 00000000..44f82bc5
--- /dev/null
+++ b/imageio/imageio-icns/src/main/resources/META-INF/services/javax.imageio.spi.ImageWriterSpi
@@ -0,0 +1 @@
+com.twelvemonkeys.imageio.plugins.icns.ICNSImageWriterSpi
diff --git a/imageio/imageio-icns/src/test/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriterTest.java b/imageio/imageio-icns/src/test/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriterTest.java
new file mode 100644
index 00000000..d1af9df7
--- /dev/null
+++ b/imageio/imageio-icns/src/test/java/com/twelvemonkeys/imageio/plugins/icns/ICNSImageWriterTest.java
@@ -0,0 +1,189 @@
+/*
+ * Copyright (c) 2017, Harald Kuhr
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ * * Neither the name of the copyright holder nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.twelvemonkeys.imageio.plugins.icns;
+
+import com.twelvemonkeys.imageio.util.ImageWriterAbstractTest;
+import org.junit.Test;
+
+import javax.imageio.IIOImage;
+import javax.imageio.ImageIO;
+import javax.imageio.ImageWriter;
+import javax.imageio.stream.ImageOutputStream;
+import java.awt.image.BufferedImage;
+import java.awt.image.RenderedImage;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.util.List;
+
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * ICNSImageWriterTest.
+ *
+ * @author <a href="mailto:harald.kuhr@gmail.com">Harald Kuhr</a>
+ * @author last modified by $Author: harald.kuhr$
+ * @version $Id: ICNSImageWriterTest.java,v 1.0 25/08/2018 harald.kuhr Exp$
+ */
+public class ICNSImageWriterTest extends ImageWriterAbstractTest {
+
+    private final ICNSImageWriterSpi provider = new ICNSImageWriterSpi();
+
+    @Override
+    protected ImageWriter createImageWriter() {
+        return provider.createWriterInstance(null);
+    }
+
+    @Override
+    protected List<? extends RenderedImage> getTestData() {
+        return asList(
+                new BufferedImage(32, 32, BufferedImage.TYPE_INT_ARGB),
+                new BufferedImage(32, 32, BufferedImage.TYPE_BYTE_BINARY),
+                new BufferedImage(32, 32, BufferedImage.TYPE_BYTE_INDEXED),
+                new BufferedImage(16, 16, BufferedImage.TYPE_INT_ARGB),
+//                new BufferedImage(48, 48, BufferedImage.TYPE_INT_ARGB), // Only supported for compression None/RLE
+                new BufferedImage(64, 64, BufferedImage.TYPE_INT_ARGB),
+                new BufferedImage(128, 128, BufferedImage.TYPE_INT_ARGB),
+                new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB),
+                new BufferedImage(512, 512, BufferedImage.TYPE_INT_ARGB),
+                new BufferedImage(1024, 1024, BufferedImage.TYPE_INT_ARGB)
+        );
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testWriteNonSquare() throws IOException {
+        // ICNS only supports square icons (except some arcane 16x12 we don't currently support)
+        ImageWriter writer = createImageWriter();
+        try (ImageOutputStream stream = ImageIO.createImageOutputStream(new ByteArrayOutputStream())) {
+
+            writer.setOutput(stream);
+
+            writer.write(new BufferedImage(32, 64, BufferedImage.TYPE_INT_ARGB));
+
+        }
+        finally {
+            writer.dispose();
+        }
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testWriteBadSize() throws IOException {
+        // ICNS only supports sizes in multiples of 2 (16, 32, 64, ..., 1024 + 48 and 96)
+        ImageWriter writer = createImageWriter();
+        try (ImageOutputStream stream = ImageIO.createImageOutputStream(new ByteArrayOutputStream())) {
+
+            writer.setOutput(stream);
+
+            writer.write(new BufferedImage(17, 17, BufferedImage.TYPE_INT_ARGB));
+
+        }
+        finally {
+            writer.dispose();
+        }
+    }
+
+    @Test
+    public void testSequencesSupported() {
+        ImageWriter writer = createImageWriter();
+        try {
+            assertTrue(writer.canWriteSequence());
+        }
+        finally {
+            writer.dispose();
+        }
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testWriteSequenceNotStarted() throws IOException {
+        // ICNS only supports sizes in multiples of 2 (16, 32, 64, ..., 1024 + 48 and 96)
+        ImageWriter writer = createImageWriter();
+        try (ImageOutputStream stream = ImageIO.createImageOutputStream(new ByteArrayOutputStream())) {
+
+            writer.setOutput(stream);
+
+            BufferedImage image = new BufferedImage(32, 32, BufferedImage.TYPE_INT_ARGB);
+            writer.writeToSequence(new IIOImage(image, null, null), writer.getDefaultWriteParam());
+
+        }
+        finally {
+            writer.dispose();
+        }
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testEndSequenceNotStarted() throws IOException {
+        // ICNS only supports sizes in multiples of 2 (16, 32, 64, ..., 1024 + 48 and 96)
+        ImageWriter writer = createImageWriter();
+        try (ImageOutputStream stream = ImageIO.createImageOutputStream(new ByteArrayOutputStream())) {
+
+            writer.setOutput(stream);
+            writer.endWriteSequence();
+        }
+        finally {
+            writer.dispose();
+        }
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testPrepareSequenceAlreadyStarted() throws IOException {
+        // ICNS only supports sizes in multiples of 2 (16, 32, 64, ..., 1024 + 48 and 96)
+        ImageWriter writer = createImageWriter();
+        try (ImageOutputStream stream = ImageIO.createImageOutputStream(new ByteArrayOutputStream())) {
+
+            writer.setOutput(stream);
+            writer.prepareWriteSequence(null);
+            writer.prepareWriteSequence(null);
+        }
+        finally {
+            writer.dispose();
+        }
+    }
+
+    @Test
+    public void testWriteSequence() throws IOException {
+        ImageWriter writer = createImageWriter();
+        ByteArrayOutputStream output = new ByteArrayOutputStream();
+
+        try (ImageOutputStream stream = ImageIO.createImageOutputStream(output)) {
+            writer.setOutput(stream);
+
+            writer.prepareWriteSequence(null);
+            for (RenderedImage image : getTestData()) {
+                IIOImage iioImage = new IIOImage(image, null, null);
+                writer.writeToSequence(iioImage, writer.getDefaultWriteParam());
+            }
+            writer.endWriteSequence();
+        }
+        finally {
+            writer.dispose();
+        }
+    }
+}
\ No newline at end of file