Version Control (or Revision Control) tools support collaborative work and provide backups to ensure that work products are not lost.

• All history is saved
• Changes can be tracked/visualized (e.g. diff)
• Concurrent modifications are prevented or at least detected
• Several versions can be developed and maintained in parallel, developers can easily switch between working on different versions (e.g. the stable branch vs. a development branch where they experiment with new features)
• VC tools support access control management to enable team collaboration

The main principle of version control is that code (or other work products) is stored in a repository that can be accessed only through specific operations:

• initialization: create and initialize a new repository
• commit: store a new version of the code in the repository. The old version is also saved.
• update: retrieve the latest version from the repository (to update one's local copy)
• revert: undo the latest commit, go back to previous version
• branch: branch out from the main sequence of versions, creating a second "current" version associated with a specific name.
• merge: make a new version from two parallel branches, the new version combining data from the two branches. There is only one branch left after that.

In the centralized model, each developer has a workspace ("working copy" of the code), and there is a single master repository that everyone contributes to.

In the decentralized model, each developer has both a local workspace and a complete VC repository locally. The developer commits to his/her local repository, and can also use the other operations defined above. However, new operations must be defined to exchange data between repositories: the main new operations are:

• clone: create a new repository by making an exact copy of another repository
• pull: update a local repository by copying over the latest commits from a remote repository.
• push: update a remote repository by copying over the latest commits from the local repository. This implies that the user has write access to the remote repository: this is typically done to update an online repository (e.g. github).

Example version control protocols: CVS, SVN (centralized), Git, Mercurial (decentralized) Online "forges", e.g. Github, Sourceforge, Gitorious, Google code, host development projects and implement different version control protocols. They are primarily for open-source code, which is typically free to host, but also host private (closed-source) repositories for a fee (this is an example of software as a service, cloud computing). Large software companies typically run their own version control servers.