Agency and communion are gender-stereotypical traits, which were explicitly designed to capture desirable attributes of men and women, respectively. Whereas the existence of gender gaps in agency and communion is commonly known, it remains unknown what the average magnitude, stability (over time and developmental age), and variability (across cultures, sampling strategies, and measures) of these gender differences are. Consistent with social role theory (Eagly, 1987; Wood & Eagly, 2012), the current meta-analysis estimated that men tended to be more agentic than women (g = 0.40, k = 928 samples, N = 254,731 participants), whereas women tended to be more communal than men (g = −0.56, k = 937 samples, N = 254,465 participants). Moderator analyses revealed that these gender differences in agency and communion have been decreasing over time. The gender gap in communion decreased with age but increased with country-level gender occupational segregation. Further, the gender gap in agency was larger when sampling participants as couples (vs. sampling as individuals), and the gaps in both agency and communion were larger in heterosexual (vs. gay/lesbian and bisexual) samples. An important methodological moderator was measurement instrument (e.g., short-form Bem Sex Role Inventory shows much smaller gender gaps than the long-form). Altogether, we leveraged a large database to reveal effects consistent with social role theory—that men are higher in agency (masculinity) and women are higher in communion (femininity)—while simultaneously offering insight into factors (earlier time period, occupational segregation, younger age, sampling in couples, heterosexual orientation) that serve to exacerbate such effects. (PsycInfo Database Record (c) 2022 APA, all rights reserved)