diff --git a/README.md b/README.md
index 81f1229..6aad26e 100644
--- a/README.md
+++ b/README.md
@@ -747,7 +747,31 @@ fs.writeFile('/myfile', buffer, function (err) {
 
 #### fs.appendFile(filename, data, [options], callback)<a name="appendFile"></a>
 
-NOTE: Not yet implemented, see https://github.com/js-platform/filer/issues/88
+Writes data to the end of a file. `data` can be a string or a buffer, in which case any encoding option is ignored. The `options` argument is optional, and can take the form `"utf8"` (i.e., an encoding) or be an object literal: `{ encoding: "utf8", flag: "w" }`. If no encoding is specified, and `data` is a string, the encoding defaults to `'utf8'`.  The callback gets `(error)`.
+
+Examples:
+
+```javascript
+// Append UTF8 text file
+fs.writeFile('/myfile.txt', "More...", function (err) {
+	if (err) throw err;
+});
+fs.appendFile('/myfile.txt', "Data...", function (err) {
+  if (err) throw err;
+});
+// '/myfile.txt' would now read out 'More...Data...'
+
+// Append binary file
+var more = new Uint8Array([1, 2, 3, 4]);
+var data = new Uint8Array([5, 6, 7, 8]);
+fs.writeFile('/myfile', more, function (err) {
+	if (err) throw err;
+});
+fs.appendFile('/myfile', buffer, function (err) {
+  if (err) throw err;
+});
+// '/myfile' would now contain [1, 2, 3, 4, 5, 6, 7, 8]
+```
 
 #### fs.setxattr(path, name, value, [flag], callback)<a name="setxattr"></a>
 
diff --git a/src/fs.js b/src/fs.js
index 31e2167..0ca1c5f 100644
--- a/src/fs.js
+++ b/src/fs.js
@@ -1308,6 +1308,17 @@ define(function(require) {
     return O_FLAGS[flags];
   }
 
+  function validate_file_options(options, enc, fileMode){
+    if(!options) {
+      options = { encoding: enc, flag: fileMode };
+    } else if(typeof options === "function") {
+      options = { encoding: enc, flag: fileMode };
+    } else if(typeof options === "string") {
+      options = { encoding: options, flag: fileMode };
+    }
+    return options;
+  }
+
   // nullCheck from https://github.com/joyent/node/blob/master/lib/fs.js
   function nullCheck(path, callback) {
     if (('' + path).indexOf('\u0000') !== -1) {
@@ -1598,13 +1609,7 @@ define(function(require) {
   }
 
   function _readFile(fs, context, path, options, callback) {
-    if(!options) {
-      options = { encoding: null, flag: 'r' };
-    } else if(typeof options === "function") {
-      options = { encoding: null, flag: 'r' };
-    } else if(typeof options === "string") {
-      options = { encoding: options, flag: 'r' };
-    }
+    options = validate_file_options(options, null, 'r');
 
     if(!nullCheck(path, callback)) return;
 
@@ -1644,7 +1649,6 @@ define(function(require) {
           callback(null, data);
         });
       });
-
     });
   }
 
@@ -1674,13 +1678,7 @@ define(function(require) {
   }
 
   function _writeFile(fs, context, path, data, options, callback) {
-    if(!options) {
-      options = { encoding: 'utf8', flag: 'w' };
-    } else if(typeof options === "function") {
-      options = { encoding: 'utf8', flag: 'w' };
-    } else if(typeof options === "string") {
-      options = { encoding: options, flag: 'w' };
-    }
+    options = validate_file_options(options, 'utf8', 'w');
 
     if(!nullCheck(path, callback)) return;
 
@@ -1714,6 +1712,41 @@ define(function(require) {
     });
   }
 
+  function _appendFile(fs, context, path, data, options, callback) {
+    options = validate_file_options(options, 'utf8', 'a');
+
+    if(!nullCheck(path, callback)) return;
+
+    var flags = validate_flags(options.flag || 'a');
+    if(!flags) {
+      callback(new EInvalid('flags is not valid'));
+    }
+
+    data = data || '';
+    if(typeof data === "number") {
+      data = '' + data;
+    }
+    if(typeof data === "string" && options.encoding === 'utf8') {
+      data = new TextEncoder('utf-8').encode(data);
+    }
+
+    open_file(context, path, flags, function(err, fileNode) {
+      if(err) {
+        return callback(err);
+      }
+      var ofd = new OpenFileDescription(fileNode.id, flags, fileNode.size);
+      var fd = fs.allocDescriptor(ofd);
+
+      write_data(context, ofd, data, 0, data.length, ofd.position, function(err2, nbytes) {
+        if(err2) {
+          return callback(err2);
+        }
+        fs.releaseDescriptor(fd);
+        callback(null);
+      });
+    });
+  }
+
   function _getxattr (context, path, name, callback) {
     if (!nullCheck(path, callback)) return;
 
@@ -2179,6 +2212,17 @@ define(function(require) {
     );
     if(error) callback(error);
   };
+  FileSystem.prototype.appendFile = function(path, data, options, callback_) {
+    var callback = maybeCallback(arguments[arguments.length - 1]);
+    var fs = this;
+    var error = fs.queueOrRun(
+      function() {
+        var context = fs.provider.getReadWriteContext();
+        _appendFile(fs, context, path, data, options, callback);
+      }
+    );
+    if(error) callback(error);
+  };
   FileSystem.prototype.lseek = function(fd, offset, whence, callback) {
     callback = maybeCallback(callback);
     var fs = this;
diff --git a/tests/spec/fs.appendFile.spec.js b/tests/spec/fs.appendFile.spec.js
new file mode 100644
index 0000000..e7187ed
--- /dev/null
+++ b/tests/spec/fs.appendFile.spec.js
@@ -0,0 +1,170 @@
+define(["Filer"], function(Filer) {
+
+  describe('fs.appendFile', function() {
+    beforeEach(function() {
+      this.db_name = mk_db_name();
+      this.fs = new Filer.FileSystem({
+        name: this.db_name,
+        flags: 'FORMAT'
+      });
+      this.fs.writeFile('/myfile', "This is a file.", { encoding: 'utf8' }, function(error) {
+        if(error) throw error;
+      });
+    });
+
+    afterEach(function() {
+      indexedDB.deleteDatabase(this.db_name);
+      delete this.fs;
+    });
+
+    it('should be a function', function() {
+      expect(typeof this.fs.appendFile).toEqual('function');
+    });
+
+    it('should append a utf8 file without specifying utf8 in appendFile', function() {
+      var complete = false;
+      var _error, _result;
+      var that = this;
+
+      var contents = "This is a file.";
+      var more = " Appended.";
+
+      that.fs.appendFile('/myfile', more, function(error) {
+        if(error) throw error;
+      });
+      that.fs.readFile('/myfile', 'utf8', function(error, data) {
+        if(error) throw error;
+        _result = data;
+        complete = true;
+      });
+
+      waitsFor(function() {
+        return complete;
+      }, 'test to complete', DEFAULT_TIMEOUT);
+
+      runs(function() {
+        expect(_error).toEqual(null);
+        expect(_result).toEqual(contents+more);
+      });
+    });
+
+    it('should append a utf8 file with "utf8" option to appendFile', function() {
+      var complete = false;
+      var _error, _result;
+      var that = this;
+
+      var contents = "This is a file.";
+      var more = " Appended.";
+
+      that.fs.appendFile('/myfile', more, 'utf8', function(error) {
+        if(error) throw error;
+      });
+      that.fs.readFile('/myfile', 'utf8', function(error, data) {
+        if(error) throw error;
+        _result = data;
+        complete = true;
+      });
+
+      waitsFor(function() {
+        return complete;
+      }, 'test to complete', DEFAULT_TIMEOUT);
+
+      runs(function() {
+        expect(_error).toEqual(null);
+        expect(_result).toEqual(contents+more);
+      });
+    });
+
+    it('should append a utf8 file with {encoding: "utf8"} option to appendFile', function() {
+      var complete = false;
+      var _error, _result;
+      var that = this;
+
+      var contents = "This is a file.";
+      var more = " Appended.";
+
+      that.fs.appendFile('/myfile', more, { encoding: 'utf8' }, function(error) {
+        if(error) throw error;
+      });
+      that.fs.readFile('/myfile', { encoding: 'utf8' }, function(error, data) {
+        if(error) throw error;
+        _result = data;
+        complete = true;
+      });
+
+      waitsFor(function() {
+        return complete;
+      }, 'test to complete', DEFAULT_TIMEOUT);
+
+      runs(function() {
+        expect(_error).toEqual(null);
+        expect(_result).toEqual(contents+more);
+      });
+    });
+
+    it('should append a binary file', function() {
+      var complete = false;
+      var _error, _result;
+      var that = this;
+
+      // String and utf8 binary encoded versions of the same thing:
+      var contents = "This is a file.";
+      var binary = new Uint8Array([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46]);
+      var more = " Appended.";
+      var binary2 = new Uint8Array([32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
+      var binary3 = new Uint8Array([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46,
+                                    32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
+
+      that.fs.writeFile('/mybinaryfile', binary, function(error) {
+        if(error) throw error;
+      });
+      that.fs.appendFile('/mybinaryfile', binary2, function(error) {
+        if(error) throw error;
+      });
+      that.fs.readFile('/mybinaryfile', 'ascii', function(error, data) {
+        if(error) throw error;
+        _result = data;
+        complete = true;
+      });
+
+      waitsFor(function() {
+        return complete;
+      }, 'test to complete', DEFAULT_TIMEOUT);
+
+      runs(function() {
+        expect(_error).toEqual(null);
+        expect(_result).toEqual(binary3);
+      });
+    });
+
+    it('should follow symbolic links', function () {
+      var complete = false;
+      var _result;
+      var that = this;
+
+      var contents = "This is a file.";
+      var more = " Appended.";
+
+      that.fs.symlink('/myfile', '/myFileLink', function (error) {
+        if (error) throw error;
+      });
+      that.fs.appendFile('/myFileLink', more, 'utf8', function (error) {
+        if (error) throw error;
+      });
+      that.fs.readFile('/myFileLink', 'utf8', function(error, data) {
+        if(error) throw error;
+        _result = data;
+        complete = true;
+      });
+
+      waitsFor(function() {
+        return complete;
+      }, 'test to complete', DEFAULT_TIMEOUT);
+
+      runs(function() {
+        expect(_result).toEqual(contents+more);
+      });
+    });
+  });
+
+});
\ No newline at end of file
diff --git a/tests/test-manifest.js b/tests/test-manifest.js
index 9b4b87a..43a549b 100644
--- a/tests/test-manifest.js
+++ b/tests/test-manifest.js
@@ -18,6 +18,7 @@ define([
   "spec/fs.open.spec",
   "spec/fs.write.spec",
   "spec/fs.writeFile-readFile.spec",
+  "spec/fs.appendFile.spec",
   "spec/fs.read.spec",
   "spec/fs.close.spec",
   "spec/fs.link.spec",