This chapter discusses positive aging from a lifespan perspective. That is, it situates later life within the life as a whole and differentiates two periods within later life – the third (young-old) and fourth (oldest-old) ages. While discussing multiple dimensions of biopsychosocial aging, which include physical and cognitive health, the chapter gives primary attention to psychosocial aging, where great potential exists for cross-fertilization with positive psychology. The chapter begins with brief discussion of demographics (i.e., the aging of societies around the globe) and definitional issues, recognizing that there are multiple traditions within gerontology that have addressed positive dimensions of the aging process. Then, employing gerontology’s distinction between the third and fourth ages of life, we discuss the potential for positive experience during the fourth age and the more extensive areas of positive functioning that characterize the third age. In closing, we identify several interventions that promote aging well and suggest ways of approaching research in this area.