Influence by Robert Cialdini

I loved it!

This is an extremely interesting nonfiction book summarizing the principles of influence. He breaks influence down into 6 main types - reciprocity, consistency, social proof, authority, liking, and scarcity. For each one, he goes over interesting, recent research, with examples.

The most striking part was his summary of an undercover investigation into an end of the world cult in the late 60s, and the strange behavior of those people, all interpreted as them trying to remain internally consistent with their reputation.