What motivates political actors to engage in European Union annulment litigation? This is the main question studied in this chapter. Our starting point is the observation that it is not possible to reduce public actors' decisions to initiate annulment actions to the pure legal characteristics of the cases. Annulment actions do not automatically arise from specific legal circumstances. This is what we learn from the examples of annulments reported in the previous chapters. There is more to filing an annulment lawsuit then just a legal-technical quarrel. This more is the political context that surrounds a concrete decision to engage in annulment litigation. While never contradicting the legal logic of annulment litigation, actors chose from the universe of potential annulment conflicts to engage in due to political reasons, which we conceive as material gains, institutional competences, ideology, or political trust. Consider in this context that annulment litigation is a defence against decisions made by an EU institution; such a supranational decision, if it remains unchallenged, constitutes a final point in a struggle about particular policy choices. In other words, if actors do not take up the fight-that is, if nobody litigates-the current interpretation of the supranational measure adopted prevails. It marks the institutional endpoint of a conflict, which can then have feedback effects. Actors obviously can choose not to engage in annulment conflict, but if their choice is to do so, it is the context of the struggle they go through in the multilevel policy CHAPTER 5