AbstractTRANSIMS is an activity-based and an integrated system of travel forecasting and microscopic simulation models developed for regional transportation planning. It uses a new paradigm of modeling individual travelers on microscopic network, thus it differs from traditional 4-step travel demand forecasting models in its underlying concepts and structure. Although TRANSIMS was originally developed for regional travel demand forecasting, the use of TRANSIMS is not limited to them. A variety of case studies and researches using TRANSIMS was being conducted in various transportation fields. This paper introduces main functions and capabilities of TRANSIMS, reviews various applications of TRANSIMS and explores future opportunities of using TRANSIMS.