We connect gender disparities in research output and collaboration patterns in economics. We first document large gender gaps in research output. These gaps persist across 50 years despite a significant increase in the fraction of women in economics during that time. We further show that output differences are closely related to differences in the co-authorship networks of men and women: women have fewer collaborators, collaborate more often with the same co-authors, and a higher fraction of their co-authors collaborate with each other. Taking into account co-authorship networks reduces the gender output gap by 18%.