Quantitative studies analysing individual differences in environmental concern (i.e., apprehension about the quality of nature and natural resources including air, water, soil and animal and plant species) have consistently found differences between men and women, whereby women are more likely to display pro-environmental attitudes, although the underlying reasons remain largely unclear. Understanding the gender gap in environmental concern is crucial for designing and targeting environmental policies and for developing environmental education programmes. This paper examines five prominent theories that address the gender gap: Socialisation theory, Economic Salience theory, Parenthood Status theory, the Class-Gender effect and Ecofeminism. Ecofeminism constitutes a theoretical perspective which, despite offering a joint analysis of feminism and environmentalism, has rarely been employed in applied research regarding the gender gap in environmental concern. Using hierarachical regression techniques and data from the World Values Survey (N = 51,763) across 45 countries, this study finds that attitudes of gender equality are positively correlated with environmental concern. The present study supports ecofeminist theory by highlighting the positive role played by gender egalitarian attitudes in environmental concern. This research is the first of its kind to study the influence of gender egalitarian attitudes on environmental concern with such a large representative sample of countries, using hierarchical models to evaluate the effect of contextual factors.