While cybercrime can often be an individual activity pursued by lone hackers, it has increasingly grown into a group activity, with networks across the world. This chapter critically examines the group element of cybercrime from several perspectives. It identifies the platforms that online groups---cybercriminal and otherwise---use to interact, and considers groups as both perpetrators and victims of cybercrime. A key novelty is the discovery of new types of online groups whose collective actions border on criminality. The chapter also analyzes how online cybercrime groups form, organize, and operate. It explores issues such as trust, motives, and means, and draws on several poignant examples, from Anonymous to LulzSec, to illustrate the arguments.