Moderation analysis is essential for understanding interaction effects, when the relationship between two variables depends on the value of a third. This chapter introduces the concept through real-world examples. After outlining common types of moderation (binary, continuous, hierarchical), the chapter walks through the key terminology, including moderators, focal predictors, and conditional effects. It covers the classic moderation model and introduces interaction terms in regression. Later sections delve into two-way and three-way interactions, providing detailed guidance on specification, estimation, and interpretation. Graphical methods for exploring interaction effects are emphasized, using interaction plots and marginal effects visualization. The chapter ensures that readers are able not only to model interaction effects correctly but also to communicate them clearly to non-technical stakeholders.