TransCAD transportation planning software offers native support for custom-built Activity-Based Models (ABM). It features a highly efficient computational platform synthesizing the advantages of multithreading and parallel processing to tackle the large populations and heavy numerical calculations associated with the most sophisticated ABMs in practice. Both traditional and state-of-the-art econometric modeling frameworks are available to the modeler, including linear regression, multinomial and nested Logit, destination choice, hazard duration and Multiple Discrete-Continuous Extreme Value (MDCEV) procedures. An easy-to-use flowchart interface allows model components to be organized and interconnected to represent the desired behavioral processes. A flexible parameter editor facilitates specification and editing of model structures, utility equations and data sources, also allowing the user to define expressions to create new variables on the fly from existing matrices and tables. All of the ABM features are integrated with the other TransCAD procedures an d tools including multi-modal traffic assignment, GIS-based data visualization, and reporting. The outputs from TransCAD ABMs can also be used directly as inputs to simulation-based Dynamic Traffic Assignment (DTA) in TransModeler.