A chorus of voices is celebrating the potential of social media and other new peer-to-peer connection technologies for teaching people about science and health in the 21st century. Rather than encouraging equity in what we all know and think about scientific discoveries, household consumer tips, the latest health recommendations, or opportunities for medical services, systematic reliance on social networks to spread information may nonetheless be a recipe for inequity. An increasing body of research suggests that people are not equal in their tendency to share information with others around them. In general, people do not take advantage of the chance to share ideas with others, a paradox in our current era of apparent information abundance. But it also appears that some people are much less likely than others to share information. Some of the differences in peer-to-peer sharing represent disparity in that information sharing is constrained unjustly by factors outside of a person’s immediate control. This book explains why these information-sharing patterns persist, why they matter to society, and what, if anything, can be done to address these tendencies.