Subversion is a version control system that is a compelling replacement for CVS in the open source community.
The package is subversion. To install it, run:
apt-get install subversion
In the Debian wiki there are two tutorials:
You can also have a look at the official manual.
Using subversion on Alioth
See Alioth/Svn for details on how to use subversion for maintaining Debian packages.
Packaging with subversion