Games are a successful pedagogical tool to change attitudes and behaviors. This chapter will examine how games facilitate change, discuss common pitfalls, and outline best practices for making serious games for clinical practice. Sustained engagement and motivation are key to lasting clinical interventions. When developing a game for clinical practice, the designer should avoid "punishing by rewards" (Kohn, 1993), damaging motivation towards the desired goal. Understanding game design principles is crucial to creating intrinsically engaging experiences that lead to lasting motivation. The Mechanics, Dynamics, and Aesthetics (MDA) framework is widely accepted by game designers as a framework to make compelling games. Using MDA as a base for understanding how to create engaging experiences, this chapter proposes a new framework for serious games called Mechanics, Dynamics, Aesthetics, and Outcomes. MDAO describes how to design a game that is intrinsically motivating and effective by focusing on the interplay between outcomes and other vectors of design.