In UML Distilled, I bemoaned the fact that there isn't a good book on teaching UML's activity diagrams. There still isn't, but I recently came across Conrad Bock's articles on UML 2.0 . Amongst these there is a series of articles on activity diagrams that go into more depth than I was able to cover in Distilled. (For those who don't know, Conrad Bock is one of the leaders of the activity diagram work in UML 2.)