This book constitutes the proceedings of the 13th International Workshop on OpenMP, IWOMP 2017, held in Stony Brook, NY, USA, in September 2017. The 23 full papers presented in this volume were carefully reviewed and selected from 28 submissions. They were organized in topical sections named: Advanced Implementations and Extensions; OpenMP Application Studies; Analyzing and Extending Tasking; OpenMP 4 Application Evaluation; Extended Parallelism Models: Performance Analysis and Tools; and Advanced Data Management with OpenMP.