Mediators and moderators are variables that affect the association between an independent variable and an outcome variable. Mediators provide additional information about how or why two variables are strongly associated. In contrast, moderators explain the circumstances that cause a weak or ambiguous association between two variables that were expected to have a strong relationship. Mediators and moderators are often overlooked in research designs, or the terms are used incorrectly. This article summarizes the conceptual differences between mediators and moderators. The statistical analysis of moderators and mediators in multiple regression is briefly described and two examples are presented.