Dissent and Departure: Why Do German MPs Leave Their Parties?

People join political parties to collaborate with like-minded individuals in realising their political objectives. However, an inherent part of party life is that members may leave when they no longer identify with the party’s aims and values. While the departure of rank-and-file members often goes unnoticed, complications arise when elected officials, such as MPs, decide to leave. This article examines the phenomenon of parliamentary group (PPG) and party switching among German MPs from 2005 to 2025, focusing on its causes, patterns, and implications. Drawing on a dataset covering all cases within this period, the study identifies key trends in German MPs' defection behaviour, including the rarity of direct transitions to other PPGs and the frequent tendency to remain unaffiliated or join minor parties after leaving their original group. Applying established theoretical frameworks for party membership exit to the unique context of MPs, the analysis considers their dual role as party members and elected representatives. It explores factors such as ideological divergence, material incentives, participation opportunities, and structural constraints within parties. Three in-depth case studies provide insights into the interplay of ideological, organisational, and strategic considerations driving these decisions. The findings contribute to a deeper understanding of internal party dynamics, the impact of defection on parliamentary representation, and the challenges such exits pose to party stability and electoral prospects.