Collective decision making seems a straightforward matter: people come together and decide. But why is it that today’s winners can turn into tomorrow’s losers? Why can’t you always get what you want? How does the interaction between the decision makers influence the outcome? And are opportunists better off than stubborn decision makers? This book takes a refreshing look at collective decision making by using models of evolutionary biology and naturalistic decision making to analyse real-world cases. These cases include the rise and fall of the Dutch high-speed railway project and the unexpected effects of introducing public-private partnerships to connect the new Thai national airport to Bangkok. Gerrits and Marks successfully guide the reader towards an in-depth understanding through rich empirical research and uncover the beautiful complexity of collective decision making. Understanding Collective Decision Making will be of great interest to academics working in public administration, political science and evolutionary theory. Public managers will also find this book helpful to understand why and how collective decisions are formed.