<b><i>Background:</i></b> Stereology is the science of inferring quantitative features of 3-dimensional structures from lower dimensional samples of those structures (probes). It is a statistical discipline and therefore may seem intimidating to many potential users. Without a proper understanding of its principles, though, errors may be made in the quantitative reporting of structural research results. <b><i>Summary:</i></b> This review article attempts to explain and justify the basic principles of stereology as applied to the glomerulus in a simple and accessible way. A few common errors in application are described. The strengths and weaknesses of “biased” (model-based) stereology are described as well as the basics of design-based (“unbiased”) stereology. <b><i>Key Messages:</i></b> Stereology is a useful body of theory and practices when quantitation of structural histological features of the glomerulus is desired.