Jim Hendler discusses social machines, which he defines as networks of machines supporting networks of people working together in ways that impact the real world. He argues that social networking consumes huge amounts of human time and that this time could be harnessed through social machines to solve problems like curing disease and feeding the hungry. Examples of early social machines include games with a purpose that harness human computation and citizen science projects like Galaxy Zoo. Moving forward, social machines may blend more with artificial intelligence, and their study requires multidisciplinary perspectives from computing, social science, and other fields. Realizing their potential faces both social challenges around online communities and technical challenges in platform design.