This chapter focuses on political campaigns' use of social media in the context of the US elections. It identifies emerging campaign practices enabled or facilitated by social media and highlights recent trends in political campaigns' use of social media between the 2008 and 2016 elections. By reviewing scientific research that empirically investigates the effects of social media on voters, the chapter discusses the role social media plays in voters' information acquisition, political discussion and participation, and voting decisions. It describes the normative implications of social media campaigns for the functioning of democracy. The rise of social media, such as Facebook, Instagram, Snapchat, Twitter, and YouTube, has set the stage for many changes in election campaign practices. The terms "Facebook election," "Snapchat election," and "Twitter politics" describe the transformation that contemporary election campaigns have undergone. While pre-social media election campaigns widely utilized digital tools such as candidate websites, they were little more than "brochureware," offering candidates an online presence.