What more do we want in modeling and simulation interoperability and reuse?

Oceans of ink have been applied to discussions of Modeling and Simulation (M&S) reuse and interoperability over the last twenty plus years. Strong business cases have been built, leading to major investments in development of standards, infrastructure, commercial products, and many successful military simulation systems. M&S interoperability and reuse have matured over the past three decades from cutting edge research, through state of the art, to today's standard practice. In this paper we describe M&S interoperability and reuse, review the state of practice, outline the productive things that can and should be pursued in this field, analyze the barriers to further progress, and propose a path forward.