We cannot imagine a political system without opposition. Despite this crucial position in politics, political science has largely neglected studying (the power of) oppositions. Attempting to fill this gap, this article analyzes the institutional opportunities of parliamentary oppositions. It offers a parsimonious framework by distinguishing two dimensions of opposition power: Some institutions enable oppositions to control governments, while others offer opportunities to present alternatives. A comparison of institutions in 21 democracies shows that countries fall into four groups along these dimensions: In majoritarian democracies, weak control mechanisms are countered by excellent opportunities to publicize alternatives. Consociational democracies are characterized by strong control mechanisms, but provide only weak opportunities to present alternatives. Moreover, in Southern Europe, control mechanisms and opportunities to present alternatives are weak, while both are pronounced in Nordic Europe. The results are summarized in three indices that can easily be applied in research examining oppositions and their power.
