This chapter situates the impact of social media on American society within the context of historical communication technologies that were equally innovative or disruptive in eras past. Facebook is an interesting and rich case study because of the effects of its unique convergence of affordances and norms on human interaction. An assessment of the contemporary role of social media in the day-to-day lives of most Americans is crucial in highlighting a fundamental aspect about Facebook engagement: people use the site to stay connected to and learn about other people. The functionalities of the site are optimized for social engagement more generally, subsuming its use for political purposes, and these aspects of the site should inform our conceptualization and measurement of political engagement on Facebook. For most people, most of the time, exposure to political information is largely incidental and occurs in a context in which they are actively seeking social information about their connections. Six distinguishing features of the content on Facebook contribute to social inference and the formation of affective attitudes: expression cues, source cues, aggregated information, endorsements, social cues, and social commentary.