This book constitutes the refereed proceedings of the 14th IFIP WG 2.13 International Conference on Open Source Systems, OSS 2018, held in Athens, Greece, in June 2018. The 14 revised full papers and 2 short papers presented were carefully reviewed and selected from 38 submissions. The papers cover a wide range of topics in the field of free/libre open source software (FLOSS) and are organized in the following thematic sections: organizational aspects of OSS projects, OSS projects validity, mining OSS data, OSS in public administration, OSS governance, and OSS reusability.