This volume contains the papers accepted for presentation at the Fourth International Symposium on Programming Language Implementation and Logic Programming (PLILP '92) held in Leuven, Belgium, August 26-28, 1992. Theaim of the symposium was to explore new declarative concepts, methods and techniques relevant for implementation of all kinds of programming languages, whether algorithmic or declarative. The symposium gathered researchers from the fields of algorithmic programming languages as well as logic, functional, and object-oriented programming. The topics discussed in the volume include: - Declarative implementation techniques; - Implementation of declarative concepts and modules;…