This text reviews a set of widely used summary inequality measures, and the lesser known relative distribution method. It provides the basic rationale behind each and discusses their interconnections. It also introduces model-based decomposition of inequality over time using quantile regression. This approach enables researchers to estimate two different contributions to changes in inequality between two time points. Key features include: clear statistical explanations that provide fundamental statistical basis for understanding the new modeling framework; straightforward empirical examples which reinforce statistical knowledge and ready-to-use procedures; and, multiple approaches to assessing inequality which are introduced by starting with the basic distributional property and providing connections among approaches. This supplementary text is appropriate for any graduate-level, intermediate, or advanced statistics course across the social and behavioral sciences, as well as individual researchers.