This paper aims at classifying and discussing the various ways along which the "object" paradigm is used in parallel and distributed contexts. We distinguish the applicative approach, the integrative approach, and the reflective approach. The applicative approach applies object-oriented concepts, as they are, to structure parallel and distributed systems through libraries. The integrative approach consists in merging concepts such as: object and activity, message passing and transaction. The reflective approach integrates protocol libraries intimately within an object-based programming language. We discuss and illustrate each of these approaches and we point out their complementary levels and goals. ANY OTHER IDENTIFYING INFORMATION OF THIS REPORT DISTRIBUTION STATEMENT First issue 35 copies. SUPPLEMENTARY NOTES REPORT DATE January 17, 1996 TOTAL NO. OF PAGES 21 WRITTEN LANGUAGE English NO. OF REFERENCES 52 DEPARTMENT OF INFORMATION SCIENCE Faculty of Science, Univ..