CVS (Concurrent Version System) is a version control system, initially released in 1990 and based on RCS (Revision Control System) from 1982. Building on the basic version control primitives provided by RCS, CVS added many higher-level functions which simplified management of large projects, focusing on manipulating groups of files rather than individual files. CVS provides developers with the ability to track changes to a project over time, to revert parts of the project to their state at an arbitrary point in time, to work on the project concurrently with other developers, and to work on different variants of the project simultaneously. CVS operations provide relatively simple ways of performing most common manipulations on a large project, while still having the flexibility that allows fairly complex version control tasks.

CVS initially did not support client-server operation, but the support was added early on, making CVS very popular in academic environments, as well as many opensource projects. Its popularity increased even more with support for authentication and encryption, and ports to many UNIX platforms, Mac OS and Windows.