Participation in many behaviors is associated with individuals’ social status and differences in access to resources, which affect their opportunities to engage in these behaviors. For example, behaviors in the health and environmental domain differ between individuals and groups of differing socioeconomic status (SES). While associations between social position and behavior are increasingly recognized and explored, relatively little is known of the mechanisms and processes by which these disparities relate to behavior change. This chapter discusses concepts of inequity relevant to behavior change, highlighting the need for consistent and meaningful operationalizations. The chapter outlines the theoretical frameworks of disparities, emphasizes the important role that multilevel perspectives of socio-structural determinants of disparities play in behavior change, and highlights how behavioral theory can help in understanding disparities in behavior change. Using health behavior examples, mechanisms underlying intervention-generated inequities are identified. If the effects of theory-based determinants on behavior differ by SES, interventions based on these determinants are likely to be differentially effective in groups differing by SES, further contributing to health disparities. Future research on behavior change should include a stronger focus on equity across domains, better document the differential effects on behavior change, and clearly specify the role of inequity in theories of behavior change.