Agenda setting and constructivism have established a very close relationship since the first studies on the transformation of an issue into a problem at the beginning of the 20th century. Why a problem becomes a problem is a complex process in which ideas and cognitive frames play a crucial role. Instead of studying the characteristics of actors participating in the agenda-setting process or the nature of the difficulties themselves – whether they are serious or mild, new or recurring, short-term or long-term – constructivist approaches concentrate on the framing of information as the crucial variable that explains why an issue makes it onto the political agenda. The aim of this chapter is to analyse the intimate, but very often implicit, relationship between constructivism and agenda setting. In the first section, the chapter presents the major claims and developments of constructivism with regard to the agenda-setting process in policy studies. In the second section, the chapter outlines the main controversies and shows how constructivism has tried to answer the limitations of other approaches in the analysis of the agenda-setting process. The third and final section develops a series of issues that might be addressed in possible research agendas, anticipating future developments.