Hackathons are Facebook's overnight innovation sessions, usually held every six or eight weeks. In Facebook's early days, hackathons involved just a few handfuls of employees. They'd order takeout and pull an all-nighter working to prototype potential new features for the social network.

Facebook hackathons have since grown into something much bigger and are now .

"The people Facebook hires are creative and want to work on interesting stuff. Hackathons give them a creative outlet on the side, outside of work," Engineering Manager Pedram Keyani says. Keyani attended his first hackathon five years ago, when he first joined Facebook, and has taken part in almost every one ever since.

"Hackathons are important to us on a number of levels," he says. "It , which is really important for innovation. Your project isn't going to be perfect. You're going to explore an idea knowing it might not be the right one--but, hey, you only spent a night working on it, and you learned something."

At Facebook, hackathons have also been instrumental in encouraging cross-company collaboration: It gives employees an opportunity to work with others they normally might not work with, Keyani says. It builds new relationships and is an opportunity to learn new skills.