The feminization of old age justifies a separate chapter on gender differences despite the fact that they are mentioned in almost every chapter, particularly in the last chapter of this book. The aim of the present chapter is to describe in which biopsychosocial variables – physical, functional, and mental health, personality, and social integration – men and women differ. As a summary statement of the empirical data base in this chapter, we can conclude the following: Gender differences found in the domains examined are small and there are few age differences (from ages 70 to over 100) within the noted gender differences. Of the 27 biopsychosocial variables, when considered separately, 14 show significant gender differences and 4 a significant age-by-gender interaction effect. Most of these differences are in the health domain. When adding the five sociodemographic variables and regarding all variables conjointly, we can correctly classify 78% of the men and 83% of the women. In this context the most significant variables are marital and educational status, physical health, and hearing – that is, not being married and having less education, as well as suffering from a musculoskeletal disease, and having good hearing significantly increase the likelihood of being an old woman. We close the chapter with the question of whether the fact of feminization of old age is rendering a discussion about gender differences in old age obsolete.