Most serious games have been developed without a proper and comprehensive design theory. To contribute to the development of such a theory, this article presents the underlying design philosophy of LEVEE PATROLLER, a game to train levee patrollers in the Netherlands. This philosophy stipulates that the design of a digital serious game is a multiobjective problem in which trade-offs need to be made. Making these trade-offs takes place in a design space defined by three equally important components: (a) Play, (b) Meaning, and (c) Reality. The various tensions between these three components result in design dilemmas and trilemmas that make it difficult to balance a serious game. Each type of tension is illustrated with one or more examples from the design of LEVEE PATROLLER. (Contains 7 figures and 1 note.)