Discussions of Health 2.0, a term first coined in 2005, were guided by three main tenets: (a) health was to involve more participation, because an evolution in the web encouraged more direct consumer engagement in their own health care; (b) data was to become the new "Intel Inside" for systems supporting the vital decisions in health; and (c) a sense of collective intelligence from the network would supplement traditional sources of knowledge in health decision making. Interests in understanding the implications of a new paradigm for patient engagement in health and health care were kindled by findings from surveys such as the National Cancer Institute's Health Information National Trends Survey, showing that patients were quick to look online for information to help them cope with disease. This article considers how these 3 facets of Health 2.0--participation, data, and collective intelligence--can be harnessed to improve the health of the nation according to Healthy People 2020 goals. The authors begin with an examination of evidence from behavioral science to understand how Web 2.0 participative technologies may influence patient processes and outcomes, for better or worse, in an era of changing communication technologies. The article then focuses specifically on the clinical implications of Health 2.0 and offers recommendations to ensure that changes in the communication environment do not detract from national (e.g., Healthy People 2020) health goals. Changes in the clinical environment, as catalyzed by the Health Information Technology for Economic and Clinical Health Act to take advantage of Health 2.0 principles in evidence-based ways, are also considered.