Why is it that many large public projects run out of control in terms of scope, budget and time? How can it be explained that urban regeneration programs are highly successful in one neighborhood but fail to deliver in an adjacent neighborhood? Why is it that public policies can return unexpected and sometimes even unwanted outcomes, despite meticulous planning? Why is public decision-making such a complex affair? The world is an erratic place, full of surprises, some of which are wanted and others are unwanted. Public decision-making in this world is like punching clouds: considerable energy is put into the punching but the cloud goes its own way, despite the punches. Recent ideas and insights from the complexity sciences improve our understanding of the intricate nature of public decision-making. This book offers a bridge between the study of public decision-making in the domain of Public Administration on the one hand, and the complexity sciences on the other hand. It is aimed at (doctoral) students and scholars in Public Administration who are curious about how the complexity sciences can inform the analysis and understanding of public decision-making. The book introduces important concepts such as systems, non-linear dynamics, self-organization and coevolution, and discusses their relevance to public decision-making. It also proposes a case-based research method for researching this complexity. Lasse Gerrits, Ph.D. is associate professor in Public Administration at the Erasmus University Rotterdam (the Netherlands) and member of the research group Governance of Complex Systems.