This paper aims at discussing and classifying the various ways in which the object paradigm is used in concurrent and distributed contexts. We distinguish among the library approach, the integrative approach, and the reflective approach. The library approach applies object-oriented concepts, as they are, to structure concurrent and distributed systems through class libraries. The integrative approach consists of merging concepts such as object and activity, message passing, and transaction, etc. The reflective approach integrates class libraries intimately within an object-based programming language. We discuss and illustrate each of these and point out their complementary levels and goals.