Stereotypically, men are considered more agentic, while women are considered more communal. In this project, we use large-scale cross-cultural data from 6,363,416 participants from 137 nations to study the size and cultural specificity of gender differences in agency and communion. Specifically, we examine three broad research questions: First, do gender differences in the agency and communion really exist? We find that across 137 nations women are slightly more communal and slightly less agentic than men. Second, are these gender differences amendable by cultural factors? We find large cross-cultural differences. Finally, which cultural factors can explain these cross-cultural differences? We competitively tested five such factors, each one derived from another extant theory on the origins of gender differences in psychological attributes. We find that gender differences in agency are highest in nations with high power distance and that gender differences in communion are highest in nations with high individualism.