In political systems where the executive is responsible to the legislature, the process and outcomes of government formation are of prime importance for democratic governance and political representation. This is especially the case when legislative elections return a parliament where no single party wins a majority of seats, as several parties are then needed to build a coalition government that relies on the confidence of a majority of members of parliament. Given the substantive and empirical importance of the subject, coalition theory applied to the making and breaking of governments is one of the most flourishing areas of research in political science. Relying on recent reviews of the field, this introductory chapter identifies remaining research gaps and provides an overview of the volume’s new developments in the study of coalition governments.