While academic researchers debate the reality or size of sex differences, people going about their daily lives see sex differences everywhere. Newspaper photographs of world leaders show only a smattering of women; personnel of day care centers are rarely men. Bookstore shelves boast titles like Men are from Mars, Women are from Venus and You Just Don’t Understand: Women and Men in Conversation. How early do children show behaviors and abilities that differ by sex? Why and how do boys and girls come to develop along different paths? Are differences as large as they might appear in media reports and best sellers? Can differences be reduced by educational interventions or social policy? Should they be? This presentation will draw from research in developmental psychology to consider the role of both biological and social processes in identifying, understanding, and modifying the development of sex differences.