NOTE Yii is now hosted on GitHub. Please get the latest code and report issues of Yii on GitHub.

Yii is a high-performance programming framework for developing Web applications in PHP 5. It enables maximum reusability in Web programming and can significantly accelerate the development process. The name Yii (pronounced as Yee or [ji:]) stands for easy, efficient and extensible.

Yii is easy to learn and use. You only need to know PHP and object-oriented programming. You are not forced to learn a new configuration or templating language.

Yii is extremely fast. Its overhead to applications written on top of it is negligible. As a matter of fact, it is one of the most efficient PHP frameworks around.

Yii is highly reusable and extensible. Yii is purely object-oriented. Everything in Yii is a self-contained component which can be configured, reused or extended easily. More importantly, Yii has an ever-increasing extension library consisting of user-contributed components, which may help reduce your development time significantly.

Yii comes with a rich set of features. From MVC, Active Record, to theming, internationalization and localization, Yii provides nearly every feature needed by today's Web 2.0 application development.

Yii has very detailed documentation. From the definitive guide to class reference, Yii has every information you need to quickly learn and master it.

Yii is carefully designed from the beginning to fit for serious Web application development. It is neither a byproduct of some project nor a conglomerate of third-party work. It is the result of the authors' rich experience of Web application development and the investigation and reflection of the most popular Web programming frameworks and applications.

Last but not least, Yii is free! Yii uses the new BSD license, and it also ensures that the third-party work it integrates with use BSD-compatible licenses. This means it is both financially and lawfully free for you to use Yii to develop either open source or proprietary applications.