Classical approach to test theory has been the foundation for educational and psychological measurement for over 90 years. This approach concerns with measurement error and hence test reliability, which in part relies on individual test items. The CTT package, developed in light of this, provides functions for test- and item-level analyses of dichotomous and polytomous response items. This review covers the basic concepts in classical theory that are related to test reliability and item analysis and demonstrates some of the key features of the CTT package while discussing its limitations.