Background: Contemporary approaches to physical activity motivation and promotion focus on explicit motivational processes which regulate intentional physical activity. Less is known about the role of implicit processes, which may be instrumental in regulating habitual aspects of unintentional (i.e., incidental) physical activity (PA).PurposeTo test the proposition that the routine nature of unintentional PA makes it amenable to control by implicit processes. Methods: Participants (N = 201) completed measures of explicit motivation (i.e., efficacy beliefs, outcome expectations, behavioral intentions, perceived behavioral control) and implicit attitudes toward physical activity, and then wore a pedometer for 1 week.ResultsImplicit attitudes positively predicted PA after controlling for well-established predictors of intentional physical activity. Conclusions: PA motivation involves both explicit and implicit processes, and PA promotion efforts may be enhanced by attending to relevant implicit motivation processes.