Creativity is individual, and it is social. The social aspects of creativity have become of increasing interest as systems have emerged that mobilize large numbers of people to engage in creative tasks. We examine research related to collective intelligence and differentiate work on collective creativity from other collective activities by analyzing systems with respect to the tasks that are performed and the outputs that result. Three types of systems are discussed: games, contests and networks. We conclude by suggesting how systems that generate collective creativity can be improved and how new systems might be constructed.