The principles of free and open source software (FOSS) are fundamental to the ethos of the communities building blockchain networks. While it is not uncommon for a single organization or small group of core developers to coordinate and deliver most of the work, the source code is generally open for everyone to inspect and improve upon. Control is maintained not by keeping software proprietary, but through social and institutional means, including ideological discourse, community management, and trademark license agreements. Despite the unique governance challenges from issuing network-specific assets to operators, investors, users, or other stakeholders, there are important similarities between blockchain networks and traditional FOSS projects. Existing research on FOSS governance may therefore prove helpful in designing blockchain governance systems.