This paper studies the conditions under which legislators become specialized in specific policy areas, while others remain generalist when speaking in parliament. A growing literature has investigated the institutional and partisan conditions that lead to different levels of floor participation. Still, it remains an open question about which topics do MPs speak when they do so. We consider that MPs’ specialization arises as a result of a dynamic interaction between MPs and their parliamentary leadership. In particular, this specialization process will be a function of rules regulating access to floor time, party leaderships’ preferences and MPs’ ambition and promotion structure. We test our arguments using the German and Spanish cases from 1996 to 2017. Concretely, we merge a comprehensive dataset of oral questions, previously coded according to the Comparative Agenda Project coding scheme, with MPs’ personal and partisan data. Preliminary results show that seniority is associated with specialization while participating in more committees leads to speaking about more topics. Interestingly, when a party platform is focused on a small set of issues (i.e niche parties), this is reflected in their MPs behaviour during the whole legislative period.