Previous research on coalition politics has found an “incumbency advantage” in government formation, but it has provided no clear explanation as to why this advantage exists. We classify existing theories as either preference-based or institutions-based explanations for why incumbent coalitions might be likely to form again, and we integrate these explanations into a coherent theoretical argument. We also claim that it is possible, to some extent, to distinguish these explanations empirically by taking into account the “historical context” of coalition bargaining. Using a comprehensive new data set on coalition bargaining in Europe, we show that coalitions, in general, are more likely to form if the parties comprising them have worked together in the recent past, and that incumbent coalitions are more likely to re-form if partners have not experienced a severe public conflict while in office together or suffered a recent setback at the polls. The incumbency advantage disappears completely if partners have become mired in conflict or have lost legislative seats (even after accounting for the impact of seat share on coalition size). Moreover, in certain circumstances, institutional rules that grant incumbents an advantage in coalition bargaining greatly enhance their ability to remain in office.