During the past decade, many parliamentary democracies have experienced bargaining delays when forming governments. The previous literature has attributed protracted government formation processes to a high degree of preference uncertainty among the political parties and a high level of bargaining complexity. The article draws on such theories, but also adds a third theoretical mechanism, commitment problems, and highlights two explanatory variables that have not received much attention so far. The first is pre-electoral coalitions, which are declarations by parties stating that they intend to collaborate with each other after the election. The second is familiarity, which is the mutual trust between parties that comes from having worked together in the past. By combining a large-N study of government formation processes in 17 West European parliamentary democracies (1945–2019) with an in-depth case study of the prolonged Swedish government formation process in 2018–2019, it is shown that pre-electoral coalitions that fail to win a majority can sometimes delay, not speed up, government formation. In addition, a lack of familiarity may sometimes lead to a breakdown of negotiations and drawn-out government formation processes.