Online health communities provide a means for patients and their families to learn about an illness, seek and offer support, and connect with others in similar circumstances. They are supported by a variety of technologies and are hosted by patients, advocacy groups, medical organizations, and corporations. Online health communities raise difficult design challenges because of the wide variability of members' expertise and needs. The importance of online health communities is evidenced by the impact they have on the quality of life and health literacy of their members and by their popularity, which is likely to increase due to changes in the health care system coupled with increased infiltration and use of the Internet. This talk will explore current trends in online health communities and the significant issues in designing and evaluating systems that help members interact with other participants and medical experts in meaningful ways.