We examine editors' influence on the scientific content of academic journals by unpacking the role of three major forces: journals' stated missions, the aggregate supply of and demand for specific topics, and scientific homophily via editorial gatekeeping. In a sample of top biomedical journals, we find the first two forces explain the vast majority of variation in published content. The upper bound of the homophily effect is statistically significant but practically much less important. Marginal changes to the composition of editorial boards do not meaningfully impact journals' content in the short run. However, we cannot rule out persistent or pervasive frictions in the publication process.