Physical inactivity is considered a major risk factor for the noncommunicable chronic illnesses and conditions that account for the majority of mortality, morbidity, and healthcare costs globally. Despite this, population-level participation in physical activity is inadequate to confer health benefits and offer protection from disease. Attitude theory and research is expected to provide an evidence base for the development of effective and sustained interventions to promote physical activity. In this chapter, I outline contemporary approaches to the conceptualization and measurement of attitudes in physical activity, the effectiveness of attitudes in predicting participation in physical activity, and evaluate the state of the evidence on the role of attitude-based interventions in promoting physical activity participation. Research adopting attitudes to predict physical activity has typically done so in the context of social cognitive models. Recent research has focused on distinct effects of implicit and explicit attitudes to behavior and the application of dual-processes frameworks to explain physical activity behavior. Intervention research has primarily focused on changing attitudes by adopting behavior-change methods targeting salient beliefs in persuasive communications to promote physical activity participation through attitude change. Few studies have explicitly tested the processes by which attitude-based interventions change physical activity behavior through the mediation of attitudes. Furthermore, little research has attempted to change attitudes toward physical activity by changing implicit attitudes. High-quality panel and intervention studies aimed at identifying the role of attitudes in changing physical activity are needed.