LPAR-21S: Editor's Preface

This volume contains the papers of IWIL-2017: The 2017 International Workshop on the Implementation of Logics, and the Short Presentation Papers of LPAR-21: The 21st International Conference on Logic for Programming, Artificial Intelligence and Reasoning. IWIL 2017 was held on the 7th May 2017, and LPAR-21 8th-12th May 2017, at Cresta Riley's Hotel in Maun, Botswana.