Sudhir Venkatesh is a professor of sociology at Columbia University and a lead writer of urban life and underground economies. Once upon a time, he was a lowly grad student looking for something more meaningful than just writing numbers. He ended up making his way to one of the poorest areas of Chicago, and long story short, became best friends with a high level leader in the Black Kings, a large gang. This book basically documents his life with his new friend and talks in detail about gang life, relationships with non-gang members in gang territory, life in large urban housing apartment complexes, etc etc etc. Basically, it's awesome. Check it out if you're interested at all in any of those topics.
PS- I picked it up for $1! Gotta love used book stores.