I have drafted this rails initialization process after thorough understanding and debugging rails lib code. I have also referred rails initialisation guide present here - Initialization guide so I tried make it simpler to understand for all of us. Here is a step by step rails initialization process. (specifically for Rails 3.1.1) Perform following steps before you start learning and understanding this process git clone https://github.com/rails/rails.git cd rails git checkout v3.1.1 Initialization Process When you do "rails s" from inside your rails app folder, it will load "script/