diff --git a/src/library/cache.cr b/src/library/cache.cr
new file mode 100644
index 0000000..00c65ba
--- /dev/null
+++ b/src/library/cache.cr
@@ -0,0 +1,159 @@
+require "digest"
+
+class InfoCache
+  alias ProgressCache = Tuple(String, Int32)
+
+  def self.clear
+    clear_cover_url
+    clear_progress_cache
+    clear_sort_opt
+  end
+
+  def self.clean
+    clean_cover_url
+    clean_progress_cache
+    clean_sort_opt
+  end
+
+  # item id => cover_url
+  @@cached_cover_url = {} of String => String
+  @@cached_cover_url_previous = {} of String => String # item id => cover_url
+
+  def self.set_cover_url(id : String, cover_url : String)
+    @@cached_cover_url[id] = cover_url
+  end
+
+  def self.get_cover_url(id : String)
+    @@cached_cover_url[id]?
+  end
+
+  def self.invalidate_cover_url(id : String)
+    @@cached_cover_url.delete id
+  end
+
+  def self.move_cover_url(id : String)
+    if @@cached_cover_url_previous[id]?
+      @@cached_cover_url[id] = @@cached_cover_url_previous[id]
+    end
+  end
+
+  private def self.clear_cover_url
+    @@cached_cover_url_previous = @@cached_cover_url
+    @@cached_cover_url = {} of String => String
+  end
+
+  private def self.clean_cover_url
+    @@cached_cover_url_previous = {} of String => String
+  end
+
+  # book.id:username => {signature, sum}
+  @@progress_cache = {} of String => ProgressCache
+  # book.id => username => {signature, sum}
+  @@progress_cache_previous = {} of String => Hash(String, ProgressCache)
+
+  def self.set_progress_cache(book_id : String, username : String,
+                              entries : Array(Entry), sum : Int32)
+    progress_cache_id = "#{book_id}:#{username}"
+    progress_cache_sig = Digest::SHA1.hexdigest (entries.map &.id).to_s
+    @@progress_cache[progress_cache_id] = {progress_cache_sig, sum}
+    Logger.debug "Progress Cached #{progress_cache_id}"
+  end
+
+  def self.get_progress_cache(book_id : String, username : String,
+                              entries : Array(Entry))
+    progress_cache_id = "#{book_id}:#{username}"
+    progress_cache_sig = Digest::SHA1.hexdigest (entries.map &.id).to_s
+    cached = @@progress_cache[progress_cache_id]?
+    if cached && cached[0] == progress_cache_sig
+      Logger.debug "Progress Cache Hit! #{progress_cache_id}"
+      return cached[1]
+    end
+  end
+
+  def self.invalidate_progress_cache(book_id : String, username : String)
+    progress_cache_id = "#{book_id}:#{username}"
+    if @@progress_cache[progress_cache_id]?
+      @@progress_cache.delete progress_cache_id
+      Logger.debug "Progress Invalidate Cache #{progress_cache_id}"
+    end
+  end
+
+  def self.move_progress_cache(book_id : String)
+    if @@progress_cache_previous[book_id]?
+      @@progress_cache_previous[book_id].each do |username, cached|
+        id = "#{book_id}:#{username}"
+        unless @@progress_cache[id]?
+          # It would be invalidated when entries changed
+          @@progress_cache[id] = cached
+        end
+      end
+    end
+  end
+
+  private def self.clear_progress_cache
+    @@progress_cache_previous = {} of String => Hash(String, ProgressCache)
+    @@progress_cache.each do |id, cached|
+      splitted = id.split(':', 2)
+      book_id = splitted[0]
+      username = splitted[1]
+      unless @@progress_cache_previous[book_id]?
+        @@progress_cache_previous[book_id] = {} of String => ProgressCache
+      end
+
+      @@progress_cache_previous[book_id][username] = cached
+    end
+    @@progress_cache = {} of String => ProgressCache
+  end
+
+  private def self.clean_progress_cache
+    @@progress_cache_previous = {} of String => Hash(String, ProgressCache)
+  end
+
+  # book.dir:username => SortOptions
+  @@cached_sort_opt = {} of String => SortOptions
+  @@cached_sort_opt_previous = {} of String => Hash(String, SortOptions)
+
+  def self.set_sort_opt(dir : String, username : String, sort_opt : SortOptions)
+    id = "#{dir}:#{username}"
+    @@cached_sort_opt[id] = sort_opt
+  end
+
+  def self.get_sort_opt(dir : String, username : String)
+    id = "#{dir}:#{username}"
+    @@cached_sort_opt[id]?
+  end
+
+  def self.invalidate_sort_opt(dir : String, username : String)
+    id = "#{dir}:#{username}"
+    @@cached_sort_opt.delete id
+  end
+
+  def self.move_sort_opt(dir : String)
+    if @@cached_sort_opt_previous[dir]?
+      @@cached_sort_opt_previous[dir].each do |username, cached|
+        id = "#{dir}:#{username}"
+        unless @@cached_sort_opt[id]?
+          @@cached_sort_opt[id] = cached
+        end
+      end
+    end
+  end
+
+  private def self.clear_sort_opt
+    @@cached_sort_opt_previous = {} of String => Hash(String, SortOptions)
+    @@cached_sort_opt.each do |id, cached|
+      splitted = id.split(':', 2)
+      book_dir = splitted[0]
+      username = splitted[1]
+      unless @@cached_sort_opt_previous[book_dir]?
+        @@cached_sort_opt_previous[book_dir] = {} of String => SortOptions
+      end
+      @@cached_sort_opt_previous[book_dir][username] = cached
+    end
+    @@cached_sort_opt = {} of String => SortOptions
+  end
+
+  private def self.clean_sort_opt
+    @@cached_sort_opt_previous = {} of String => Hash(String, SortOptions)
+  end
+end
diff --git a/src/library/entry.cr b/src/library/entry.cr
index b5e582f..cbebf7f 100644
--- a/src/library/entry.cr
+++ b/src/library/entry.cr
@@ -44,6 +44,8 @@ class Entry
         MIME.from_filename? e.filename
     end
     file.close
+
+    InfoCache.move_cover_url @id
   end
 
   def to_slim_json : String
@@ -81,6 +83,8 @@ class Entry
 
   def cover_url
     return "#{Config.current.base_url}img/icon.png" if @err_msg
+    cached_cover_url = InfoCache.get_cover_url @id
+    return cached_cover_url if cached_cover_url
 
     unless @book.entry_cover_url_cache
       TitleInfo.new @book.dir do |info|
@@ -96,6 +100,7 @@ class Entry
         url = File.join Config.current.base_url, info_url
       end
     end
+    InfoCache.set_cover_url @id, url
     url
   end
 
@@ -178,6 +183,11 @@ class Entry
   # For backward backward compatibility with v0.1.0, we save entry titles
   #   instead of IDs in info.json
   def save_progress(username, page)
+    InfoCache.invalidate_progress_cache @book.id, username
+    @book.parents.each do |parent|
+      InfoCache.invalidate_progress_cache parent.id, username
+    end
+
     TitleInfo.new @book.dir do |info|
       if info.progress[username]?.nil?
         info.progress[username] = {@title => page}
diff --git a/src/library/library.cr b/src/library/library.cr
index 30e93b2..2638ffd 100644
--- a/src/library/library.cr
+++ b/src/library/library.cr
@@ -102,6 +102,8 @@ class Library
 
     storage = Storage.new auto_close: false
 
+    InfoCache.clear
+
     (Dir.entries @dir)
       .select { |fn| !fn.starts_with? "." }
       .map { |fn| File.join @dir, fn }
@@ -115,6 +117,8 @@ class Library
         @title_ids << title.id
       end
 
+    InfoCache.clean
+
     storage.bulk_insert_ids
     storage.close
 
diff --git a/src/library/title.cr b/src/library/title.cr
index aa4a479..14b5754 100644
--- a/src/library/title.cr
+++ b/src/library/title.cr
@@ -60,6 +60,10 @@ class Title
     @entries.sort! do |a, b|
       sorter.compare a.title, b.title
     end
+
+    InfoCache.move_cover_url @id
+    InfoCache.move_progress_cache @id
+    InfoCache.move_sort_opt @dir
   end
 
   def to_slim_json : String
@@ -230,6 +234,9 @@ class Title
   end
 
   def cover_url
+    cached_cover_url = InfoCache.get_cover_url @id
+    return cached_cover_url if cached_cover_url
+
     url = "#{Config.current.base_url}img/icon.png"
     readable_entries = @entries.select &.err_msg.nil?
     if readable_entries.size > 0
@@ -241,10 +248,12 @@ class Title
         url = File.join Config.current.base_url, info_url
       end
     end
+    InfoCache.set_cover_url @id, url
     url
   end
 
   def set_cover_url(url : String)
+    InfoCache.invalidate_cover_url @id
     TitleInfo.new @dir do |info|
       info.cover_url = url
       info.save
@@ -252,6 +261,8 @@ class Title
   end
 
   def set_cover_url(entry_name : String, url : String)
+    selected_entry = @entries.find { |entry| entry.display_name == entry_name }
+    InfoCache.invalidate_cover_url selected_entry.id if selected_entry
     TitleInfo.new @dir do |info|
       info.entry_cover_url[entry_name] = url
       info.save
@@ -273,8 +284,13 @@ class Title
   end
 
   def deep_read_page_count(username) : Int32
-    load_progress_for_all_entries(username).sum +
-      titles.flat_map(&.deep_read_page_count username).sum
+    # CACHE HERE
+    cached_sum = InfoCache.get_progress_cache @id, username, @entries
+    return cached_sum unless cached_sum.nil?
+    sum = load_progress_for_all_entries(username).sum +
+          titles.flat_map(&.deep_read_page_count username).sum
+    InfoCache.set_progress_cache @id, username, @entries, sum
+    sum
   end
 
   def deep_total_page_count : Int32
@@ -422,6 +438,11 @@ class Title
   end
 
   def bulk_progress(action, ids : Array(String), username)
+    InfoCache.invalidate_progress_cache @id, username
+    parents.each do |parent|
+      InfoCache.invalidate_progress_cache parent.id, username
+    end
+
     selected_entries = ids
       .map { |id|
         @entries.find &.id.==(id)
diff --git a/src/library/types.cr b/src/library/types.cr
index 4e83135..094cb64 100644
--- a/src/library/types.cr
+++ b/src/library/types.cr
@@ -35,12 +35,15 @@ class SortOptions
   end
 
   def self.from_info_json(dir, username)
+    cached_opt = InfoCache.get_sort_opt dir, username
+    return cached_opt if cached_opt
     opt = SortOptions.new
     TitleInfo.new dir do |info|
       if info.sort_by.has_key? username
         opt = SortOptions.from_tuple info.sort_by[username]
       end
     end
+    InfoCache.set_sort_opt dir, username, opt
     opt
   end
 
diff --git a/src/util/web.cr b/src/util/web.cr
index 5704ea8..5e873ca 100644
--- a/src/util/web.cr
+++ b/src/util/web.cr
@@ -120,6 +120,7 @@ macro get_and_save_sort_opt(dir)
 
     sort_opt = SortOptions.new sort_method, is_ascending
 
+    InfoCache.set_sort_opt {{dir}}, username, sort_opt
     TitleInfo.new {{dir}} do |info|
       info.sort_by[username] = sort_opt.to_tuple
       info.save