CodeIgniter is an Application Development Framework - a toolkit - for people who build web sites using PHP. Its goal is to enable you to develop projects much faster than you could if you were writing code from scratch, by providing a rich set of libraries for commonly needed tasks, as well as a simple interface and logical structure to access these libraries. CodeIgniter lets you creatively focus on your project by minimizing the amount of code needed for a given task. CodeIgniter is an open source rapid development web application framework, for use in building dynamic web sites with PHP. The first public version of CodeIgniter was released on February 28, 2006, and the latest stable version 2.2.0 was released June 5, 2014.
CodeIgniter is loosely based on the popular Model-View-Controller development pattern. While controller classes are a necessary part of development under CodeIgniter, models and views are optional.
CodeIgniter is most often noted for its speed when compared to other PHP frameworks. In a critical take on PHP frameworks in general, PHP creator Rasmus Lerdorf noted that he liked CodeIgniter "because it is faster, lighter and the least like a framework."