diff --git a/README.md b/README.md
index 928d38a..c1bc748 100644
--- a/README.md
+++ b/README.md
@@ -57,7 +57,7 @@ API documentation is available [here](https://bitchan.github.io/bitmessage/docs/
     - [x] getRipe
     - [x] fromRandom
     - [ ] fromPassphrase
-  - [ ] UserAgent
+  - [x] UserAgent
   - [ ] Message
     - [ ] encrypt
     - [ ] decrypt
diff --git a/lib/index.js b/lib/index.js
index dfcd472..e19c0f0 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -19,3 +19,5 @@ exports.POW = require("./pow");
 
 /** [Working with addresses.]{@link module:bitmessage/address} */
 exports.Address = require("./address");
+/** [User Agent.]{@link module:bitmessage/user-agent} */
+exports.UserAgent = require("./user-agent");
diff --git a/lib/structs.js b/lib/structs.js
index 6d3bb52..20ae40d 100644
--- a/lib/structs.js
+++ b/lib/structs.js
@@ -38,6 +38,7 @@ var message = exports.message = {
 
   /**
    * Decode message structure.
+   * NOTE: `payload` is copied, `rest` references input buffer.
    * @param {Buffer} buf - Buffer that starts with encoded message
    * structure
    * @return {{command: string, payload: Buffer, length: number, rest: Buffer}}
@@ -99,6 +100,7 @@ var message = exports.message = {
 var var_int = exports.var_int = {
   /**
    * Decode `var_int`.
+   * NOTE: `rest` references input buffer.
    * @param {Buffer} buf - A buffer that starts with encoded `var_int`
    * @return {{value: number, length: number, rest: Buffer}}
    * Decoded `var_int` structure.
@@ -191,6 +193,7 @@ var var_int = exports.var_int = {
 exports.var_str = {
   /**
    * Decode `var_str`.
+   * NOTE: `rest` references input buffer.
    * @param {Buffer} buf - A buffer that starts with encoded `var_str`
    * @return {{str: string, length: number, rest: Buffer}}
    * Decoded `var_str` structure.
@@ -226,6 +229,7 @@ exports.var_str = {
 exports.var_int_list = {
   /**
    * Decode `var_int_list`.
+   * NOTE: `rest` references input buffer.
    * @param {Buffer} buf - A buffer that starts with encoded
    * `var_int_list`
    * @return {{list: number[], length: number, rest: Buffer}}
@@ -421,6 +425,7 @@ var SECP256K1_TYPE = 714;
 exports.encrypted = {
   /**
    * Decode encrypted payload.
+   * NOTE: all structure members are copied.
    * @param {Buffer} buf - A buffer that contains encrypted payload
    * @return {Object} Decoded encrypted structure.
    */
diff --git a/lib/user-agent.js b/lib/user-agent.js
new file mode 100644
index 0000000..4f893b3
--- /dev/null
+++ b/lib/user-agent.js
@@ -0,0 +1,84 @@
+/**
+ * Working with Bitmessage user agents.
+ * @see {@link https://bitmessage.org/wiki/User_Agent}
+ * @module bitmessage/user-agent
+ */
+
+"use strict";
+
+var var_str = require("./structs").var_str;
+var BM_NAME = require("../package.json").name;
+var BM_VERSION = require("../package.json").version;
+
+/**
+ * Decode user agent stack.
+ * NOTE: Decoding is rather loose and non-strict, it won't fail on bad
+ * user agent format because it's not that important.
+ * Also note that `rest` references input buffer.
+ * @param {Buffer} buf - A buffer that starts with encoded user agent
+ * @return {{software: Object[], length: number, rest: Buffer}}
+ * Decoded user agent structure.
+ */
+exports.decode = function(buf) {
+  var decoded = var_str.decode(buf);
+  var software = [];
+  if (decoded.str) {
+    software = decoded.str.slice(1, -1).split("/");
+    software = software.map(function(str) {
+      // That's more readable than /([^:]*)(?::([^(]*)(?:\(([^)]*))?)?/
+      var soft = {name: str};
+      var semicolon = soft.name.indexOf(":");
+      if (semicolon !== -1) {
+        soft.version = soft.name.slice(semicolon + 1);
+        soft.name = soft.name.slice(0, semicolon);
+        var obracket = soft.version.indexOf("(");
+        if (obracket !== -1) {
+          soft.comments = soft.version.slice(obracket + 1);
+          soft.version = soft.version.slice(0, obracket);
+          var cbracket = soft.comments.indexOf(")");
+          if (cbracket !== -1) {
+            soft.comments = soft.comments.slice(0, cbracket);
+          }
+        }
+      }
+      return soft;
+    });
+  }
+  return {software: software, length: decoded.length, rest: decoded.rest};
+};
+
+/**
+ * Encode user agent. Most underlying software comes first.
+ * @param {Object[]} software - List of software to encode
+ * @return {Buffer} Encoded user agent.
+ */
+var encode = exports.encode = function(software) {
+  var ua = software.map(function(soft) {
+    var version = soft.version || "0.0.0";
+    var str = soft.name + ":" + version;
+    if (str.comments) {
+      str += "(" + comments + ")";
+    }
+    return str;
+  }).join("/");
+  return var_str.encode("/" + ua + "/");
+};
+
+/**
+ * Encode bitmessage's user agent.
+ * @return {Buffer} Encoded user agent.
+ */
+exports.encodeSelf = function() {
+  return encode([{name: BM_NAME, version: BM_VERSION}]);
+};
+
+/**
+ * Encode user agent with bitmessage's user agent underneath. Most
+ * underlying software comes first.
+ * @param {Object[]} software - List of software to encode
+ * @return {Buffer} Encoded user agent.
+ */
+exports.encodeSelfWith = function(software) {
+  software = [{name: BM_NAME, version: BM_VERSION}].concat(software);
+  return encode(software);
+};
diff --git a/test.js b/test.js
index 3fb16ee..f640d90 100644
--- a/test.js
+++ b/test.js
@@ -19,6 +19,7 @@ var pubkeyFeatures = structs.pubkeyFeatures;
 var WIF = bitmessage.WIF;
 var POW = bitmessage.POW;
 var Address = bitmessage.Address;
+var UserAgent = bitmessage.UserAgent;
 
 describe("Crypto", function() {
   it("should implement SHA-512 hash", function() {
@@ -377,4 +378,44 @@ describe("High-level classes", function() {
       });
     }
   });
+
+  describe("User Agent", function() {
+    var pybm = {name: "PyBitmessage", version: "0.4.4"};
+    var bnode = {name: "bitchan-node", version: "0.0.1"};
+    var bweb = {name: "bitchan-web"};
+
+    it("should decode", function() {
+      var ua = var_str.encode("/cBitmessage:0.2(iPad; U; CPU OS 3_2_1)/AndroidBuild:0.8/");
+      var res = UserAgent.decode(ua);
+      expect(res.software).to.deep.equal([
+        {name: "cBitmessage", version: "0.2", comments: "iPad; U; CPU OS 3_2_1"},
+        {name: "AndroidBuild", version: "0.8"},
+      ]);
+      expect(res.length).to.equal(58);
+      expect(res.rest.toString("hex")).to.equal("");
+    });
+
+    it("should encode", function() {
+      var ua = UserAgent.encode([pybm]);
+      expect(var_str.decode(ua).str).to.equal("/PyBitmessage:0.4.4/");
+      var res = UserAgent.decode(ua);
+      expect(res.software).to.deep.equal([pybm]);
+      expect(res.length).to.equal(21);
+      expect(res.rest.toString("hex")).to.equal("");
+    });
+
+    it("should encode bitmessage's user agent", function() {
+      var res = UserAgent.decode(UserAgent.encodeSelf())
+      var software = res.software;
+      expect(software[0].name).to.equal("bitmessage");
+      expect(software[0]).to.have.property("version");
+
+      res = UserAgent.decode(UserAgent.encodeSelfWith([bnode, bweb]));
+      software = res.software;
+      expect(software[0].name).to.equal("bitmessage");
+      expect(software[1]).to.deep.equal(bnode);
+      expect(software[2].name).to.equal(bweb.name);
+      expect(software[2].version).to.equal("0.0.0");
+    });
+  });
 });