diff --git a/README.md b/README.md
index 33f5ed9..0fd47a2 100644
--- a/README.md
+++ b/README.md
@@ -1,24 +1,69 @@
 # ReallySimpleCaptcha
 
-TODO: Write a gem description
+ReallySimpleCaptcha is just another captcha gem.
 
-## Installation
+## Requirements
 
-Add this line to your application's Gemfile:
-
-    gem 'really_simple_captcha'
-
-And then execute:
-
-    $ bundle
-
-Or install it yourself as:
-
-    $ gem install really_simple_captcha
+- Rails >= 3
+- RMagick
 
 ## Usage
 
-TODO: Write usage instructions here
+### PlainCaptcha
+
+The plain captcha display an image with distorted text and a text field.
+
+To use it, add this line in the view file within the form tag :
+```
+<%= plain_captcha_tag %>
+```
+
+To verify the captcha in the controller, use :
+```
+plain_captcha_valid?
+```
+
+### ReverseCaptcha
+
+The reverse captcha add a text field hidden with CSS to trick bot into filling this field.
+
+To use it, add this line in the view file within the form tag :
+```
+<%= reverse_captcha_tag %>
+```
+
+To verify the captcha in the controller, use :
+```
+reverse_captcha_valid?
+```
+
+## Configuration
+
+ReverseCaptcha and PlainCaptcha must be configured separately.
+
+### PlainCaptcha
+```
+ReallySimpleCaptcha::Captcha::PlainCaptcha.configure do |config|
+  config.text_length = 6
+
+  # colors
+  config.fill = 'darkblue'
+  config.background_color = 'white'
+  # font size
+  config.pointsize = 22
+  # image modification options
+  config.implode_amount = 0.2
+  config.wave_amplitude = 4.0
+  config.wave_length = 60.0
+end
+```
+
+### ReverseCaptcha
+```
+ReallySimpleCaptcha::Captcha::ReverseCaptcha.configure do |config|
+  config.field_name = 'reverse_captcha'
+end
+```
 
 ## Contributing