With an immense increase in research, development, and application of object- oriented simulation (OOS) over the past decade, there is evidence that this technology is becoming the choice for modeling large, complex, and/or distributed systems. This paper discusses the features of OOS that dispose it to modeling these types of systems and compares the OOS approach with traditional simulation approaches. A review of OOS languages and environments is followed by a discussion of current issues pertaining to object- oriented simulation.