Three high-level observations set the stage: • Cancer is a major cause of death • Health-related concerns drive the greatest use of the Internet (Eysenbach, 2003) • Cancer patients may find support from online discussion groups. Actually, these discussion groups are for more than patients. Definitions of the users of the discussion systems and the types of systems are presented next. Care givers are those people who help a patient as friends or family of the patient (this is in contrast to care providers, who are healthcare professionals). The discussion systems to be addressed here serve both care givers and patients, and sometimes a more extended group of people who want to help or otherwise be involved in cancer support. This extended group of people will be denoted by the term ‘patient’ throughout the remainder of this article. The first patient online discussion system benefited from early technology to exploit e-mail connections known as e-mail list servers (listservs). A listserv allows a group of people to communicate by e-mail through a common email address. The listserv stores the messages received and participants can either receive e-mails one by one as they are sent, or in digests at daily, weekly or monthly intervals. Moderators are typically assigned to listservs and may determine conditions for membership in the listserv. The listserv itself has features for people to request enrollment and search the archives. Following the popularity of the World Wide Web (Web), technologists implemented Web discussion systems that allow people to register on the Web and gain access to Web-based archives of messages. These Web discussion systems typically also incorporate all the features of a listserv. Cancer patients participating in various online discussion systems will next be studied according to: • Patient patterns of use • Impact of the discussion systems on the patients • The extent to which patients might make scientific discoveries • The role of different healthcare industry entities in the management of these discussion systems The reader will see the opportunities for extended use of these discussion systems.