Nested Git repositories?

You may be looking for the Git feature called submodules. This feature helps you manage dependent repositories that are nested inside your main repository.

Place your third party libraries in a separate repository and use submodules to associate them with the main project. Here is a walk-through:

http://git-scm.com/book/en/Git-Tools-Submodules

In deciding how to segment a repo I would usually decide based on how often I would modify them. If it is a third-party library and only changes you are making to it is upgrading to a newer version then you should definitely separate it from the main project.

Just for completeness:

There is another solution, I would recommend: subtree merging.

In contrast to submodules, it's easier to maintain. You would create each repository the normal way. While in your main repository, you want to merge the master (or any other branch) of another repository in a directory of your main directory.

$ git remote add -f OtherRepository /path/to/that/repo
$ git merge -s ours --no-commit OtherRepository/master
$ git read-tree --prefix=AnyDirectoryToPutItIn/ -u OtherRepository/master
$ git commit -m "Merge OtherRepository project as our subdirectory"`

Then, in order to pull the other repository into your directory (to update it), use the subtree merge strategy:

$ git pull -s subtree OtherRepository master

I'm using this method for years now, it works :-)

More about this way including comparing it with sub modules may be found in this git howto doc.