AbstractAs preprints become integrated into conventional avenues of scientific communication, it’s critical to understand who is included and who is not. However, little is known about which countries are participating or how they collaborate with each other. Here, we present an analysis of all 67,885 preprints posted on bioRxiv (through 2019) using the first comprehensive dataset of country-level preprint author affiliations. We find the plurality of preprints (39%) come from the United States, and that countries such as the U.S. and U.K. are overrepresented on bioRxiv relative to their overall scientific output, while countries including China, Russia, and Turkey show lower bioRxiv adoption. We describe a set of “contributor countries” including Uganda, Croatia and Thailand that appear almost exclusively as non-senior authors on international collaborations. Lastly, we find multiple journals that publish a disproportionate number of preprints from some countries, a dynamic that almost always benefits manuscripts from the U.S.