Pragmatic Version Control Using Subversion

Author: Mike Mason

http://www.pragprog.com/titles/svn2/pragmatic-version-control-using-subversion

Although this is not Cocoa- or iPhone-specific, some sort of version control should be part of your development workflow.  Subversion comes with every Leopard or Snow Leopard Mac and integrates with Xcode.

I found that this book explained the core concepts behind Subversion very clearly, even if you have no prior experience with version control systems.  It also works well as a reference for times when I can't remember the exact command line syntax for a particular operation.