This report summarizes the presentations, discussions, and outcomes of the ECOOP’2000 Workshop on Object Interoperability, held in Sophia Antipolis, France, on Monday, June 12, 2000. Divided into four main sessions, the workshop covered some of the most important issues related to object interoperability at different levels (such as protocols or semantics). This report has two main goals. First, it tries to provide a snapshot of some of the current research being carried out within the object-oriented community in these areas. And second, it summarizes some of the open questions and issues related to object interoperability, in order to set the basis for further research activities.