Discusses polytomous item response theory models and the research that has been conducted to investigate a variety of possible operational procedures (item bank, item selection, trait estimation, stopping rule) for polytomous model-based computerized adaptive testing (PCAT). Studies are reviewed that compared PCAT systems based on competing item response theory models that are appropriate for the same measurement objective, as well as applications of PCAT in marketing and educational psychology. Directions for future research using PCAT are suggested.