While popular platforms developed by knowledge-producing communities such as Wikipedia and Linux co-exist and compete with alternatives such as Encyclopedia Britannica and Microsoft Windows, we understand little about how such competition affects those communities. The authors develop a theory where competition has a divergent effect on community members’ contribution—it deters potential new members from joining the community and contributing, but motivates established members to increase their contributions. To test this theory, they examine how community members’ contributions to OpenStreetMap (a widely-used digital mapping platform) changed following the competitive entry of Google Maps. We exploit the phased entry of Google Maps in different countries over time to isolate the effect of competition and our findings support our theory on the divergent effects of competition. They also find that social interaction among community members attenuates the deterrent effect of competition on potential new members, but strengthens the motivating effect of competition on established members. The authors discuss the implications for research on contributions to knowledge-producing communities, platform competition, and the effect of competition on organizations.