This is a critical design paper offering a possible scenario of use intended to provoke reflection about values and politics of design in persuasive computing. We describe the design of a system—Fit4Life—that encourages individuals to address the larger goal of reducing obesity in society by promoting individual healthy behaviors. Using the Persuasive Systems Design Model [26], this paper outlines the Fit4Life persuasion context, the technology, its use of persuasive messages, and an experimental design to test the system’s efficacy. We also contribute a novel discussion of the ethical and sociocultural considerations involved in our design, an issue that has remained largely unaddressed in the existing persuasive technologies literature [29]. Author Keywords Persuasive technology, weight loss, social implications, critical design. ACM Classification Keywords K.4.0 Computers and Society: General. H.5.2 [Information Interfaces and Presentation (e.g. HCI)]: User Interfaces – the...