Serious games need to reflect reality to achieve their purpose, whether learning, training, or provoking a behavioral change. At the same time, serious games employ features that make gaming a self-motivating, engaging, and fantastic activity. This chapter presents a conceptual model to support the design of serious games that deals with the balance between fidelity and play. Design science research guided the model development. Fidelity was conceived as a field force that attracts fun, motivation, and engagement. The model arranged the game elements into three major groups: the Game-World, the Interaction-World, and the Player's-World. Fidelity can assume different levels in each of these worlds. The Fidelity and Play model (FP) allows a holistic view of the relationship and balance between fidelity and play in a serious game.