This chapter summarized knowledge about the physical SC, a variable that has assumed great importance in studying how self-esteem is related to physical activity participation. It discussed the advantages of employing component scales such as physical SCs, and reviewed research and theory on the development of the physical SC, age and sex differences, and relationships with life adjustment. Skill development and self-enhancement research were summarized. Leading physical SC scales were briefly reviewed. A thesis of the chapter is that SE and its associations with physical activity participation can be studied best by the employment of models that are hierarchical in their structure, and which contain SC components ranging from very specific to very broad constructs. This has implications for item and inventory selection and for an ultimate understanding of how physical activity leads to mental and emotional benefits.