How to merge two independent git repositories

I have two independent repositories (A and B) and would like to merge one repo. (B) into another one (A) with keeping the whole history of both. What do to?

With git it appeared to be a very easy task.

cd A

git remote add test ../B && git fetch test

git merge test/master

git push (if you use a remote repo.)

That's it.

You can also merge a subdir of one repo. into another. But to do so you need to use git filter-branch.

I love git! ;)