Connecting to recent debate and the growing attention to the party politics of foreign policy, the chapter introduces the content and methodology of the Parliamentary Deployment Votes Database, which collects votes on military missions across a set of eleven countries in Europe and America. The chapter discusses the problems related to defining the scope of the database against divergent voting practices in national parliaments and disparate data availability, a.k.a. defining what matters in data collection and what not. It expounds how clustering into party families helps to structure collected data and theorize it, what to do with regional parties, and how to make further sense of data using voting-shares, cabinet level, and government-opposition variables. The chapter also shows how Hix et al.’s Agreement Index, used in European Studies, can be handled to measure agreement and dissent on military missions.