will use it for larger projects, like finding funding, but even more established companies correspond frequently with their Y Combinator colleagues. "There is a sort of implicit understanding that you help the other founders if and when you can," Aberman says. At various times he has called on Brian Chesney, CEO of Airbnb, and Drew Houston of Dropbox for advice and insight. Seibel says that he uses the Y Combinator list for contacts and references. "I wanted an introduction to the CEO of Tumblr, and got an introduction there," Seibel says. "In the past I've asked for introductions to insurance people, and that's worked out great. It's also great that we still reach out to Paul [Graham] for strategic questions."