The microsimulation modeling technique has become more popular over the past few years. In the area of Social Security research alone, there are now at least four major modeling efforts in the Washington, DC area and all have contributed to the Social Security policy debate in important ways. A microsimulation model starts with individual-level data that form a representative sample of the population and projects demographic and economic outcomes for that sample through time. With more microsimulation models being used in research and policy, and the level of complexity in those models on the rise, it is important for researchers and practitioners to share their research and their techniques with others. This session brings together researchers working on four major microsimulation models to discuss the current state of microsimulation and current techniques being used. The session should have broad implications for researchers and practitioners working—or hoping to work—on microsimulation models. Such techniques might also be valuable for researchers in other areas—such as those working with longitudinal data—where researchers are facing similar challenges.