This course provides the basics of item response theory and examines the use of Item Response Theory (IRT) models for test construction and ability estimation. Concepts, models and features are discussed. The item characteristic curve and the estimation of parameters, test characteristic curves, ability estimation and item and test information functions are treated. Assessment of model fit and efficiency functions are described. Models for tests with dichotomous items are covered and discussions include advantages and disadvantages of IRT relative to Classical Test Theory. Models for tests with polytomous and mixed items are covered. Other topics include the detection of differential item functioning (or item bias), and the role of IRT in Computer Adaptive Testing (CAT). The various approaches to assessment of item fit and a discussion of their strengths and weaknesses is made. The identification and comparison of the various software packages currently available for IRT applications are made. Use is made of at least two different packages and the outputs interpreted.