What are the principles that make societal problems socio-technically complex? And, even more important, how can we support public policymaking in the wake of socio-technical complexity? In The Princess in the Castle, the author investigates if, why and how serious games and game-like simulations (SGs) can support integrated policy making and planning, especially in relation to managing rivers and oceans. She argues that ‘playful methods’ are particularly suited to surround sophisticated analysis with extensive participation. The book contains many examples and illustrations but centres on: the Climate Game, used in a neighbourhood reconstruction project incorporating climate adaptation measures; The Blokkendoos Planning Kit, used in the Netherlands’ planning project Room for the River for integrated flood management; the MSP Challenge, used to further the development of integrated, eco-system based marine spatial planning. The book provides a de- and re-construction of the ‘principles of play’ that underlying integrated policy analysis. The perceived usefulness of game-like tools in the Dutch and Chinese policy contexts is empirically studied. The author concludes that serious games for policy-making and planning are powerful methods with largely untapped potential. Yet, without room to play they can be easily turn into ineffective and expensive toys. Qiqi Zhou is a researcher at Delft University of Technology, the Netherlands. She is involved in several research projects with Dutch and Chinese universities.