This volume constitutes the thoroughly refereed post-conference proceedings of the 17th International Conference on Applications of Declarative Programming and Knowledge Management, INAP 2007, and the 21st Workshop on Logic Programming, WLP 2007, held in Würzburg, Germany, during October 4-6, 2007. The 16 thoroughly revised full papers presented together with 1 invited paper were carefully reviewed and selected from numerous submissions. The topics covered are constraints; databases and data mining; extensions of logic programming; and system demonstrations.