This article expands the scope of agenda-building research, which has traditionally focused on the ability of press releases, press conferences, and political ads to influence media coverage. In-depth interviews with political reporters and editors at US newspapers during the 2012 campaign found that tweets from political leaders are used by journalists in ways that suggest first- and second-level agenda building. Participants gave examples of how political tweets have shaped their coverage in terms of the events they cover, the sources they interview, the quotes they use, and the background information they rely on to decide how to cover an issue. In addition, political tweets that contribute the most to coverage tend to have several elements in common.