The widespread diffusion of social media in recent years has created a number of opportunities and challenges for health and risk communication. Blogs and microblogs are specific forms of social media that appear to be particularly important. Blogs are webpages authored by an individual or group in which entries are published in reverse chronological order; microblogs are largely similar, but limited in the total number of characters that may be published per entry. Researchers have begun exploring the use and consequences of blogs and microblogs among individuals coping with illness as well as for health promotion. Much of this work has focused on better understanding people’s motivations for blogging about illness and the content of illness blogs. Coping with the challenges of illness and connecting with others are two primary motivations for authoring an illness blog, and blogs typically address medical issues (e.g., treatment options) and the author’s thoughts and feelings about experiencing illness. Although less prevalent, there is also evidence that illness blogging can be a resource for social support and facilitate coping efforts. Researchers studying the implications of blogs and microblogs for health promotion and risk communication have tended to focus on the use of these technologies by health professionals and for medical surveillance. Medical professionals appear to compose a noteworthy proportion of all health bloggers. Moreover, blogs and microblogs have been shown to serve a range of surveillance functions. In addition to being used to follow illness outbreaks in real-time, blogs and microblogs have offered a means for understanding public perceptions of health and risk-related issues including medical controversies. Taken as whole, contemporary research on health blogs and microblogs underscores the varied and important functions of these forms of social media for health and risk communication.