Many long-term services, e.g., weight-loss programs, require that customers comply with instructions, provide the inputs, and thus co-create a major portion of the service. This article investigates the role of public commitment in influencing motivation and behavior in a weight-loss setting. The role of susceptibility to normative influence (SNI) is also examined. The publicness with which a commitment to weight loss is made has a significant and favorable impact on long-term weight-loss compliance behavior. Short- and long-term public commitment resulted in higher levels of weight-loss motivation and higher levels of weight loss. Weight-loss motivation partly mediates the effect of public commitment on weight loss, while SNI moderates the effect of public commitment on weight loss. © 2009 Wiley Periodicals, Inc.