Measurement models developed by Georg Rasch are renowned in social science disciplines such as education, psychology and sociology. In this introduction to the models, the focus is on the simple logistic model, which is one of the most elementary and commonly used.The author explains the general principles behind the models, and demonstrates their procedures for measurement. Comparisons are made with other more widely-used measurement models. Throughout the text, an example from a personality inventory is used to provide continuity as the statistical arguments are presented and procedures explained.