While seeing a fair number of recommendations for Pro Git, I also saw a few for Git Internals, also by Scott Chacon. Thinking this might, well, focus on the internals more, I read it. It's a PDF ebook. It's not bad, and it does put earlier emphasis on internals, but doesn't real cover the internals in any more depth than Pro Git. Basically, this is the predecessor to Pro Git, and the rewrite is superior. It's fine, but if someone says to read it, read Pro Git instead.