Editorial journalism and newspapers’ editorial opinions represent an area of research that can make an important contribution to our understanding of the relationship between the press and politics. Editorials are a distinctive format and are the only place in a newspaper where the opinions of a paper as an organization are explicitly represented. Newspapers and the journalists who write editorials play a powerful role in constructing political debate in the public sphere. They use their editorial voice to attempt to influence politics either indirectly, through reaching public opinion, or directly, by targeting politicians. Editorial journalism is at its most persuasive during elections, when newspapers traditionally declare support for candidates and political parties. Despite the potential of editorial opinions to influence democratic debate, and controversy over the way newspapers and their proprietors use editorials to intervene in politics, editorial journalism is under-researched. Our understanding of the significance of this distinctive form of journalism can be better understood by exploring four key themes. First, asking “What is editorial journalism?” establishes the context of editorial journalism as a unique practice with opinion-leading intentions. Several characteristics of editorial journalism distinguish it from other formats and genres. Editorials (also known as leading articles) require a distinctive style and form of expression, occupy a special place in the physical geography of a newspaper, represent the collective institutional voice of a newspaper rather than that of an individual, have no bylines in the majority of countries, and are written with differing aims and motivations to news reports. The historical development of journalism explains the status of editorials as a distinctive form of journalism. Professional ideals and practices evolved to demand objectivity in news reporting and the separation of fact from opinion. Historically, editorial and advocacy journalism share an ethos for journalism that endeavors to effect social or political change, yet editorial journalism is distinctive from other advocacy journalism practices in significant ways. Editorials are also an integral part of the campaign journalism practiced by some newspapers. Second, research and approaches in the field of political communication have attributed a particularly powerful role to editorial journalism. Rooted in the effects tradition, researchers have attributed an important role to editorials in informing and shaping debate in the public sphere in four ways: (1) as an influence on readers, voters, and/or public opinion; (2) as an influence on the internal news agendas and coverage of newspapers; (3) as an influence on the agendas and coverage in other news media; and (4) as an influence on political or policy agendas. Theorizing newspapers as active and independent political actors in the political process further underpins the need to research editorial journalism. Third, editorial journalism has been overlooked by sociological studies of journalism practices. Research provides a limited understanding of the routines and practices of editorial journalists and the organization of editorial opinion at newspapers. Although rare, studies focusing on editorial journalism show that editorial opinion does not simply reflect the influence of proprietors, as has often been assumed. Rather, editorial opinions are shaped by a complex range of factors. Finally, existing research trajectories and current developments point to new challenges and opportunities for editorial journalism. These challenges relate to how professional norms respond to age-old questions about objectivity, bias, and partisanship in the digital age.