organizing multiple repositories with dependencies

I am looking to track some projects using Git with each project as a separate repository. Even after reading the documentation, I am still wondering if there is a way to organize things as described below.

Consider 2 projects, Project-a and Project-b, which are housed in repositories Repo-a and Repo-b respectively.  Project-a develops reusable libraries which are needed by Project-b (otherwise Project-b will not compile). When a new stable version of Project-a libraries has to be delivered, they are "checked into" a path in Repo-a. Now, I would like to setup Repo-b so that when someone starts working on Project-b, he should be able to retrieve the code from Repo-b as well as the libraries from Repo-a. Is there any way to achieve that in Git?

Thanks for any pointers!