This volume contains a selection of papers presented at the 15th International Conference on Applications of Declarative Programming and Knowledge M- agement, INAP 2004, and the 18th Workshop on Logic Programming, WLP 2004, which were held jointly in Potsdam, Germany, from March 4th to 6th, 2004. Declarative programming is an advanced paradigm for the modeling and solving of complex problems. This specification method has become more and more attractive in recent years, for example, in the domains of databases, for the processing of natural language, for the modeling and processing of combinatorial problems, and for establishing knowledge-based systems for the Web. The INAP conferences provide a forum for intensive discussions of appli- tions of important technologies around logic programming, constraint problem solving, and closely related advanced software. They comprehensively cover the impact of programmable logic solvers in the Internet society, its underlying te- nologies, and leading-edge applications in industry, commerce, government, and social services. The Workshops on Logic Programming are the annual meeting of the Society for Logic Programming (GLP e.V.). They bring together researchers interested in logic programming, constraint programming, and related areas like databases and artificial intelligence. Previous workshops have been held in Germany, A- tria, and Switzerland. Thetopicsof theselectedpapersofthisyear’sjointconferenceconcentrateon three currently important fields: knowledge management and decision support, constraint programming and constraint solving, and declarative programming and Web-based systems.