This document summarizes a talk on virtual communities. The talk discusses how social groups form in virtual worlds like Second Life, with members bonding over shared interests and identities. Virtual communities serve both game and social goals for their members. Successful communities establish norms, hierarchies, and reputation systems. The talk uses Second Life as a case study, describing communities there focused on issues like government, disabilities, and fundraising. Virtual communities operate similarly to real-world groups and can transfer relationships offline, while also providing opportunities for businesses to engage distributed audiences.