The focus of this volume is ``Heterogeneous Knowledge and Problem Solving Integration'', i.e. the combined use of different knowledge representation and problem solving paradigms.This is a central topic for the design and implementation of problem solving systems, since, from a pragmatic and engineering standpoint, the solution of a large class of problems cannot take place within one single representation language or problem solving paradigm. Heterogeneous systems represent not only a pragmatic answer, but also a theoretical alternative to the homogeneous paradigms.