This book constitutes the refereed proceedings of the 9th International IFIP WG 2.13 Conference on Open Source Systems, OSS 2013, held in Koper-Capodistria, Slovenia, in June 2013. The 18 revised full papers and 3 short papers presented were carefully reviewed and selected. The papers are organized in topical sections on innovation and sustainability; practices and methods; FOSS technologies; security and open standards; and business models and licensing.