This book constitutes the thoroughly refereed joint post-proceedings of the 15th International Conference on Applications of Declarative Programming and Knowledge Management, INAP 2004, and the 18th Workshop on Logic Programming, WLP 2004, held jointly in Potsdam, Germany in March 2004.The 18 revised full papers presented together with an invited tutorial lecture and an invited paper were selected during two rounds of reviewing and improvement. The papers are organized in topical sections on knowledge management and decision support, constraint programming and constraint solving, and declarative programming and Web-based systems.