Abstract. Parliamentary democracy has been widely embraced by politicians and especially by the scholarly community but remains less widely understood. In this essay, I identify the institutional features that define parliamentary democracy and suggest how they can be understood as delegation relationships. I propose two definitions: one minimal and one maximal (or ideal–typical). In the latter sense, parliamentary democracy is a particular regime of delegation and accountability that can be understood with the help of agency theory, which allows us to identify the conditions under which democratic agency problems may occur. Parliamentarism is simple, indirect, and relies on lessons gradually acquired in the past. Compared to presidentialism, parliamentarism has certain advantages, such as decisional efficiency and the inducements it creates toward effort. On the other hand, parliamentarism also implies disadvantages such as ineffective accountability and a lack of transparency, which may cause informational inefficiencies. And whereas parliamentarism may be particularly suitable for problems of adverse selection, it is a less certain cure for moral hazard. In contemporary advanced societies, parliamentarism is facing the challenges of decaying screening devices and diverted accountabilities.