This chapter for the first time shows what populist and non-populist politicians think about the rise and the success of populism and how they respond and interpret this political reality. The chapter examines the reactions of mainstream politicians to the rise of populism and of populist politicians to established politics in 11 countries. Drawing on in-depth qualitative interviews with some 50 politicians, the chapter explores popular definitions of populism; reasons for popularity; issues related to populism; consequences of populism; and perceptions of media support for populism. It finds that populism is seen by most mainstream politicians as a threat to the political and social order and something that needs to be challenged, while populists are keen to show how out of touch mainstream politics is. When asked for the reasons for populist success, politicians mainly point to the malfunctioning of established democratic institutions, including mainstream political parties, in addressing problems and producing convincing discourses and solutions. Politicians generally agree that the media are an important part of the equation in explaining populist success, although there is little consensus on this. Overall, there are no clear, discernible regional patterns. Instead, national contexts seem to play a major role for the workings of populism as viewed by the interviewed politicians.