Castleman gives a good historical introduction to graffiti and it's beginnings, his interviews are with the main writers of the time, such as Lee, and so this is a strong review of how it all started. It is the main text referenced in sociological writing about graffiti, but does not contain much sociological analysis itself. It was an interesting read, but obviously the graffiti scene has changed a lot since it was written! I would recommend it as a starting point for study, or just a read if your interested in the origins of graffiti culture.