Logic programming has emerged over the last 15 years as one of most promising new programming paradigms and as a very active research area. The PROGLOG experience has shown that relevant problems in areas such as expert systems, deductive databases, knowledge representation, and rapid prototyping can profitably be tackled by logic programming technology. It has also known that the performance of PROGLOG systems can be made comparable with the more traditional programming languages by means of sophisticated optimization and implementation of the design of a new class of languages, the concurrent logic lanuages. Many recent advances in the theory of logic programs are related to extension of the basic positive logic language and the related semantic problems. The original non-monotonic negation-as-failure rle has been extended in various ways and provided with new declarative characterizations. Other new language constructs are constrainsts (which lead to a very important extension of the paradignm which allows us to compute on new domains), concurrency, and modules and objects. This volume, written by a team of international experts, goes beyond the classical theory to discuss the many recent advances for the first time in a systematic form.