This book constitutes the refereed proceedings of the 9th IFIP WG 5.11 International Symposium on Environmental Software Systems, ISESS 2011, held in Brno, Czech Republic, in June 2011. The 68 revised full papers presented together with four invited talks were carefully reviewed and selected from numerous submissions. The papers are organized in the following topical sections: eEnvironment and cross-border services in digital agenda for Europe; environmental information systems and services - infrastructures and platforms; semantics and environment; information tools for global environmental assessment; climate services and environmental tools for urban planning and climate change - applications and services.