This chapter examines the define stage of the regulatory policy cycle. The define stage refers to the processes by which the issue is defined, its causes and key attributes diagnosed and the desired future state—the regulatory objectives—is set. The chapter also examines how the policy agenda is set before moving on to issue diagnosis and objective setting. Agenda-setting is a critical component of the regulatory policy process. The main mechanism through which the media impacts agenda-setting is by influencing public opinion. Agenda-setting is competitive and adversarial. Social progress too can trigger issues appearing on the governmental agenda. The governmental agenda and, ultimately, the decision agenda, are shaped by people and groups that actively compete to impose their understanding and perspective of the issue or its solution upon the public and government decision-makers. The selection of government agency therefore reflects a choice of the functional, professional or cultural lens through which the issue diagnosis is to be conducted.