diff --git a/README b/README
deleted file mode 100644
index b397b14..0000000
--- a/README
+++ /dev/null
@@ -1 +0,0 @@
-TODO: Documentation
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..d80a458
--- /dev/null
+++ b/README.md
@@ -0,0 +1,126 @@
+ReCaptcha for Rails - With AJAX Validation
+==========================================
+
+Purpose
+-------
+
+This plugin implements view helpers to generate ReCaptcha code,
+to interface with the HTTP API for captcha verification, a DSL
+to generate a `before_filter` and the necessary hacky code to
+implement AJAX captcha validation.
+
+Implementation
+--------------
+
+For AJAX validation, a request to ReCaptcha HTTP server must be
+made in order to verify the user input, but captchas can be
+checked only once.
+
+The plugin thus, in case of a successful verification, uses
+`Rails.cache` to cache the result and then the before filter
+checks the cache without issuing a second request to the
+ReCaptcha HTTP service.
+
+Installation
+------------
+
+    script/plugin install git://github.com/Panmind/recaptcha.git
+
+Gems will follow soon, hopefully after the July 22nd Ruby Social Club in Milan.
+
+Usage
+-----
+
+In your config/environment.rb:
+
+    Panmind::Recaptcha.set(
+      :private_key => 'your private key',
+      :public_key  => 'your public key
+    )
+
+In your controller, say, the `UsersController` for a signup action:
+
+    require_valid_captcha :only => :create
+
+    private
+      def invalid_captcha
+        @user = User.new params[:user]
+        @user.errors.add_to_base('Captcha failed')
+
+        render :new, :layout => 'login'
+      end
+
+The `invalid_captcha` method is called by the plugin when captcha
+verification fails, and *must* be overwritten or a `NotImplementedError`
+exception will be thrown.
+
+In your view:
+
+    <%= recaptcha :label => 'Are you human?', :theme => 'clean' %>
+
+You can pass any `RecaptchaOptions` valid option, as stated by the
+service documentation. The only nonstandard option `:label` is used
+by the plugin to print a label before the captcha widget.
+
+
+AJAX Validation
+---------------
+
+To cache the results of a successful captcha verification, a cache
+key is needed: this is generated by a `proc` passed to the `:ajax`
+option of the `require_valid_captcha` controller method. E.g.:
+
+    require_valid_captcha :only => :create, :ajax => proc { params[:email] }
+
+This will use the user submitted e-mail as a cache key. When the
+form is validated via AJAX, the eventual successful result will
+be cached; when the form is submitted, the result will be fetched
+from the cache and the signup will continue.
+
+On Panmind we use our `jquery.ajax-validation` plugin, that you
+can download from http://github.com/Panmind/jquery-ajax-nav and
+the Javascript code located in the `js/signup-sample.js` file.
+
+On the backend, an example checker that returns different HTTP
+status code follows:
+
+    def signup_checker
+      if params[:email].blank?
+        render :nothing => true, :status => :bad_request and return
+      end
+
+      email = CGI.unescape(params[:email])
+
+      # more thorough checks on email should go here
+
+      if User.exists?(['email = ?', email])
+        render :nothing => true, :status => :not_acceptable and return
+      end
+
+      unless valid_captcha?
+        invalid_captcha and return
+      end
+
+      save_solved_captcha
+      render :nothing => true, :status => :ok
+    end
+
+Moreover, the client Javascript code should be informed via an
+HTTP status when validation fails, thus the `invalid_captcha`
+must contain a special `render` when the request comes from XHR:
+
+    def invalid_captcha
+      render :nothing => true, :status => 412 and return true if request.xhr?
+      # Same invalid_captcha code as above
+    end
+
+
+Bugs
+----
+
+The `:ajax` option is clumsy, and should not require the user to pass
+a proc with semantics that are closely tied to the method that requires
+captcha verification.
+
+Maybe the `authenticity_token` is a good fit for a validation cache key?
+