Here's how I view the checkout command: It is used to check out stuff from your git database into your working tree. Stuff here means either the whole tree or some files in it. You can check out a whole tree (branch) by specifying its sha1, or you can check out a single file by specifying the tree and the filename. The fact that checkout can be used to create a branch is just a convenience because most of the time it's easier to give the tree sha1 a name to refer to for further git commands.