This document discusses continuous integration in PHP development. It explains that continuous integration helps detect problems early through immediate unit testing of all code changes. This prevents integration issues and allows developers to work incrementally with quick feedback. The document recommends writing unit tests with PHPUnit and using tools like PHP Code Sniffer to check code quality. It also discusses code coverage analysis and copy/paste detection to reduce code duplication. Finally, it provides examples of continuous integration environments like CruiseControl that can automate building and testing of PHP applications.