*Comprehensive, accessible text, updated: 40% new material includes a new chapter on multilevel IRT models, new material on loglinear models, and more. *Shows how to apply IRT by using common datasets across chapters. *Companion website provides datasets, software links, and additional resources. *Works through the examples using both free and commercially available software programs. *Of particular interest in the U.S., the U.K., Scandinavia, the Netherlands, Germany, China, and Korea.