Version control system

This is the most basic and the most important requirement for implementing CI. A Version Control System, sometimes also called a Revision Control System, is a tool to manage your code history. It can be centralized or distributed. Some of the famous centralized version control systems are SVN and IBM Rational ClearCase. In the distributed segment, we have tools like GIT and Mercurial.

Ideally, everything that is required to build software must be version controlled. A version control tool offers many features, such as tagging, branching, and so on.