The control function is one of the oldest and most fundamental spheres of representative body’s activity. The aim of the control carried out by the representative body is to in- vestigate certain areas of government activity, detect and indicate irregularities, as well as to undertake measures to prevent irregularities in the future. The implementation of the Sejm’s control function, which is based on art. 95, paragraph 2 of the Constitution, occurs when applying wide range of instruments among which we can discern in- struments of individual control of Deputies (parliamentary interpellation, parliamentary questions, questions on current affairs and current information), the activities of Sejm committees, including the parliamentary commission of inquiry and instruments of control carried out by the entire chamber. The effectiveness of these instruments may be considered on many grounds – from the possibility of being used by groups staying in opposition to the ruling majority to assessment of the objectives connected to each of the control instruments, and this requires Sejm control criteria to be defined.