Background: Smoking is recognized as the largest, single, preventable cause of death and disease in the developed world. Whilethe majority of smokers report wanting to quit, and many try each year, smokers find it difficult to maintain long-term abstinence.Behavioral support, such as education, advice, goal-setting, and encouragement, is known to be beneficial in improving thelikelihood of succeeding in a quit attempt, but it remains difficult to effectively deliver this behavioral support and keep the patientengaged with the process for a sufficient duration. In an attempt to solve this, there have been numerous mobile apps developed,yet engagement and retention have remained key challenges that limit the potential effectiveness of these interventions. Videogames have been clearly linked with the effective delivery of health interventions, due to their capacity to increase motivationand engagement of players. Objective: The objective of this study is to describe the design and development of a smartphone app that is theory-driven, andwhich incorporates gaming characteristics in order to promote engagement with content, and thereby help smokers to quit. Methods: Game design and development was informed by a taxonomy of motivational affordances for meaningful gamifiedand persuasive technologies. This taxonomy describes a set of design components that is grounded in well-established psychologicaltheories on motivation. Results: This paper reports on the design and development process of Quittr, a mobile app, describing how game designprinciples, game mechanics, and game elements can be used to embed education and support content, such that the app actuallyrequires the user to access and engage with relevant educational content. The next stage of this research is to conduct a randomizedcontrolled trial to determine whether the additional incentivization game features offer any value in terms of the key metrics ofengagementhow much content users are consuming, how many days users are persisting with using the app, and what proportionof users successfully abstain from smoking for 28 days, based on user-reported data and verified against a biochemical baselineusing cotinine tests. Conclusions: We describe a novel, and theoretically-informed mobile app design approach that has a broad range of potentialapplications. By using the virtual currency approach, we remove the need for the game to comprehensively integrate the healthyactivity as part of its actual play mechanics. This opens up the potential for a wide variety of health problems to be tackled throughgames where no obvious play mechanic presents itself. The implications of this app are that similar approaches may be of benefitin areas such as managing chronic conditions (diabetes, heart disease, etc), treating substance abuse (alcohol, illicit drugs, etc),diet and exercise, eating disorders (anorexia, bulimia, and binge eating), and various phobias.