diff --git a/cli.js b/cli.js
index 255910c..98a1354 100755
--- a/cli.js
+++ b/cli.js
@@ -7,20 +7,23 @@ var assign = require('lodash.assign');
 
 var generate = require('./lib/generate');
 var markdown = require('./lib/markdown');
-var getUserInfo = require('./lib/github');
+var updateContributors = require('./lib/contributors');
 
 var cwd = process.cwd();
 var defaultRCFile = path.join(cwd, '.all-contributorsrc');
 
 var argv = require('yargs')
+  .help('help')
+  .alias('h', 'help')
   .command('generate', 'Generate the list of contributors')
   .usage('Usage: $0 generate')
   .command('add', 'add a new contributor')
   .usage('Usage: $0 add <username> <contribution>')
   .demand(2)
-  .default('config', defaultRCFile)
   .default('file', 'README.md')
   .default('contributorsPerLine', 7)
+  .default('contributors', [])
+  .default('config', defaultRCFile)
   .config('config', function(configPath) {
     try {
       return JSON.parse(fs.readFileSync(configPath, 'utf-8'));
@@ -31,7 +34,6 @@ var argv = require('yargs')
       }
     }
   })
-  .help('help')
   .argv;
 
 argv.file = path.join(cwd, argv.file);
@@ -52,19 +54,19 @@ function onError(error) {
   }
 }
 
-if (argv[0] === 'generate') {
+var command = argv._[0];
+
+if (command === 'generate') {
   startGeneration(argv, onError);
-} else if (argv[0] === 'add') {
-  // Fetch user
-  argv.username = argv._[1];
-  argv.contributions = argv._[2].split(',');
-  getUserInfo(argv.username, function(error, user) {
+} else if (command === 'add') {
+  var username = argv._[1];
+  var contributions = argv._[2];
+  // Add/update contributor and save him to the config file
+  updateContributors(argv, username, contributions, function(error, contributors) {
     if (error) {
-      return console.error(error);
+      return onError(error);
     }
-    // TODO
-    // Add him to the contributors
-    // Save rc file with updated contributors key
+    argv.contributors = contributors;
     startGeneration(argv, onError);
   });
 }
diff --git a/lib/configFile.js b/lib/configFile.js
new file mode 100644
index 0000000..1c9ca86
--- /dev/null
+++ b/lib/configFile.js
@@ -0,0 +1,28 @@
+'use strict';
+
+var fs = require('fs');
+var _ = require('lodash/fp');
+
+function formatCommaFirst(o) {
+  return JSON.stringify(o, null, 2)
+    .split(/(,\n\s+)/)
+    .map(function (e, i) {
+      return i%2 ? '\n'+e.substring(4)+', ' : e
+    })
+    .join('');
+}
+
+function readConfig(configPath) {
+  return JSON.parse(fs.readFileSync(configPath, 'utf-8'));
+}
+
+function writeContributors(configPath, contributors, cb) {
+  var config = readConfig(configPath);
+  var content = _.assign(config, { contributors: contributors });
+  return fs.writeFile(configPath, formatCommaFirst(content), cb);
+}
+
+module.exports = {
+  readConfig: readConfig,
+  writeContributors: writeContributors
+}
diff --git a/lib/contributors/add.js b/lib/contributors/add.js
new file mode 100644
index 0000000..e86f5f0
--- /dev/null
+++ b/lib/contributors/add.js
@@ -0,0 +1,57 @@
+'use strict';
+
+var _ = require('lodash/fp');
+
+function matchContribution(type) {
+  return function(existing) {
+    return type === existing || type === existing.type;
+  };
+}
+
+function uniqueTypes(contribution) {
+  return contribution.type || contribution;
+}
+
+function formatContributions(options, existing, newTypes) {
+  var types = newTypes.split(',');
+  if (options.url) {
+    return (existing || []).concat(types.map(function(type) {
+      return { type: type, url: options.url };
+    }));
+  }
+  return _.uniqBy(uniqueTypes, (existing || []).concat(types));
+}
+
+function updateContributor(options, contributor, contributions) {
+  return _.assign(contributor, {
+    contributions: formatContributions(options, contributor.contributions, contributions)
+  });
+}
+
+function updateExistingContributor(options, username, contributions) {
+  return options.contributors.map(function(contributor, index) {
+    if (username !== contributor.login) {
+      return contributor;
+    }
+    return updateContributor(options, contributor, contributions);
+  });
+}
+
+function addNewContributor(options, username, contributions, infoFetcher, cb) {
+  infoFetcher(username, function(error, userData) {
+    if (error) {
+      return cb(error);
+    }
+    var contributor = _.assign(userData, {
+      contributions: formatContributions(options, [], contributions)
+    });
+    return cb(null, options.contributors.concat(contributor));
+  });
+}
+
+module.exports = function addContributor(options, username, contributions, infoFetcher, cb) {
+  if (_.find({login: username}, options.contributors)) {
+    return cb(null, updateExistingContributor(options, username, contributions));
+  }
+  return addNewContributor(options, username, contributions, infoFetcher, cb);
+}
diff --git a/lib/contributors/add.test.js b/lib/contributors/add.test.js
new file mode 100644
index 0000000..cc301d9
--- /dev/null
+++ b/lib/contributors/add.test.js
@@ -0,0 +1,161 @@
+import test from 'ava';
+import addContributor from './add';
+
+function mockInfoFetcher(username, cb) {
+  return cb(null, {
+    login: username,
+    name: 'Some name',
+    avatar_url: 'www.avatar.url',
+    html_url: 'www.html.url'
+  });
+}
+
+function fixtures() {
+  const options = {
+    contributors: [{
+      login: 'login1',
+      name: 'Some name',
+      avatar_url: 'www.avatar.url',
+      html_url: 'www.html.url',
+      contributions: [
+        'code'
+      ]
+    }, {
+      login: 'login2',
+      name: 'Some name',
+      avatar_url: 'www.avatar.url',
+      html_url: 'www.html.url',
+      contributions: [
+        { type: 'blog', url: 'www.blog.url/path' },
+        'code'
+      ]
+    }]
+  };
+  return {options};
+}
+
+test.cb('should callback with error if infoFetcher fails', t => {
+  t.plan(1);
+
+  const {options} = fixtures();
+  const username = 'login3';
+  const contributions = ['doc'];
+  function infoFetcher(username, cb) {
+    return cb(new Error('infoFetcher error'));
+  }
+
+  return addContributor(options, username, contributions, infoFetcher, function(error) {
+    t.is(error.message, 'infoFetcher error');
+    t.end();
+  });
+});
+
+test.cb('should add new contributor at the end of the list of contributors', t => {
+  t.plan(3);
+
+  const {options} = fixtures();
+  const username = 'login3';
+  const contributions = 'doc';
+
+  return addContributor(options, username, contributions, mockInfoFetcher, function(error, contributors) {
+    t.notOk(error);
+    t.is(contributors.length, 3);
+    t.same(contributors[2], {
+      login: 'login3',
+      name: 'Some name',
+      avatar_url: 'www.avatar.url',
+      html_url: 'www.html.url',
+      contributions: [
+        'doc'
+      ]
+    });
+    t.end();
+  });
+});
+
+test.cb('should add new contributor at the end of the list of contributors with a url link', t => {
+  t.plan(3);
+
+  const {options} = fixtures();
+  const username = 'login3';
+  const contributions = 'doc';
+  options.url = 'www.foo.bar';
+
+  return addContributor(options, username, contributions, mockInfoFetcher, function(error, contributors) {
+    t.notOk(error);
+    t.is(contributors.length, 3);
+    t.same(contributors[2], {
+      login: 'login3',
+      name: 'Some name',
+      avatar_url: 'www.avatar.url',
+      html_url: 'www.html.url',
+      contributions: [
+        { type: 'doc', url: 'www.foo.bar' }
+      ]
+    });
+    t.end();
+  });
+});
+
+test.cb(`should not update an existing contributor's contributions where nothing has changed`, t => {
+  t.plan(2);
+
+  const {options} = fixtures();
+  const username = 'login2';
+  const contributions = 'blog,code';
+
+  return addContributor(options, username, contributions, mockInfoFetcher, function(error, contributors) {
+    t.notOk(error);
+    t.same(contributors, options.contributors);
+    t.end();
+  });
+});
+
+test.cb(`should update an existing contributor's contributions if a new type is added`, t => {
+  t.plan(3);
+
+  const {options} = fixtures();
+  const username = 'login1';
+  const contributions = 'bug';
+
+  return addContributor(options, username, contributions, mockInfoFetcher, function(error, contributors) {
+    t.notOk(error);
+    t.is(contributors.length, 2);
+    t.same(contributors[0], {
+      login: 'login1',
+      name: 'Some name',
+      avatar_url: 'www.avatar.url',
+      html_url: 'www.html.url',
+      contributions: [
+        'code',
+        'bug'
+      ]
+    });
+    t.end();
+  });
+});
+
+test.cb(`should update an existing contributor's contributions if a new type is added with a link`, t => {
+  t.plan(3);
+
+  const {options} = fixtures();
+  const username = 'login1';
+  const contributions = 'bug';
+  options.url = 'www.foo.bar';
+
+  return addContributor(options, username, contributions, mockInfoFetcher, function(error, contributors) {
+    t.notOk(error);
+    t.is(contributors.length, 2);
+    t.same(contributors[0], {
+      login: 'login1',
+      name: 'Some name',
+      avatar_url: 'www.avatar.url',
+      html_url: 'www.html.url',
+      contributions: [
+        'code',
+        { type: 'bug', url: 'www.foo.bar' },
+      ]
+    });
+    t.end();
+  });
+});
diff --git a/lib/github.js b/lib/contributors/github.js
similarity index 67%
rename from lib/github.js
rename to lib/contributors/github.js
index 5396495..6a239a8 100644
--- a/lib/github.js
+++ b/lib/contributors/github.js
@@ -1,5 +1,6 @@
 'use strict';
 
+var _ = require('lodash/fp');
 var request = require('request');
 
 module.exports = function getUserInfo(username, cb) {
@@ -12,6 +13,7 @@ module.exports = function getUserInfo(username, cb) {
     if (error) {
       return cb(error);
     }
-    return cb(null, JSON.parse(res.body));
+    var user = JSON.parse(res.body);
+    return cb(null, _.pick(['login', 'name', 'avatar_url', 'html_url'], user));
   });
 }
diff --git a/lib/contributors/index.js b/lib/contributors/index.js
new file mode 100644
index 0000000..3dd5430
--- /dev/null
+++ b/lib/contributors/index.js
@@ -0,0 +1,16 @@
+'use strict';
+
+var add = require('./add');
+var github = require('./github');
+var configFile = require('../configFile');
+
+module.exports = function addContributor(options, username, contributions, cb) {
+  add(options, username, contributions, github, function(error, contributors) {
+    if (error) {
+      return cb(error);
+    }
+    configFile.writeContributors(options.config, contributors, function(error) {
+      return cb(error, contributors);
+    });
+  });
+};
diff --git a/package.json b/package.json
index c2a859f..c9029e6 100644
--- a/package.json
+++ b/package.json
@@ -24,7 +24,7 @@
   },
   "homepage": "https://github.com/jfmengels/all-contributors-cli#readme",
   "dependencies": {
-    "lodash": "^4.5.1",
+    "lodash": "^4.6.1",
     "lodash.assign": "^4.0.4",
     "lodash.findindex": "^4.2.0",
     "lodash.template": "^4.2.1",