This book constitutes revised selected papers from the 21st International Conference on Applications of Declarative Programming and Knowledge Management, INAP 2017, the 31st Workshop on Logic Programming, WLP 2017, and the 25th Workshop on Functional and (Constraint) Logic Programming, WFLP 2017. The 12 full papers presented in this volume were carefully reviewed and selected from 26 submissions. The contributions were organized in topical sections named: constraints; declarative systems; and functional and logic programming.