Martin Gross addresses a research gap with this study by systematically and comparatively examining coalition formations in large cities in general, and specifically between the CDU and Alliance 90/The Greens. He demonstrates for the first time the transferability of theories regarding municipal coalition formation processes and expands them with specific local factors. Furthermore, the study identifies necessary prerequisites for the formation of black-green coalitions and typical behavioral patterns of the actors during coalition negotiations and the design of coalition agreements.