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 {\em applicative} approach,
the {\em integrative} approach, and the {\em 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.