This chapter explores the fundamental principles and applications of matching techniques in epidemiological research. Matching is a methodological approach used to control confounding by pairing or grouping study subjects based on selected characteristics. We examine two primary forms of matching: frequency matching, which balances the distribution of confounders across groups, and individual matching, where subjects are matched one-to-one or one-to-many. Additionally, advanced techniques such as the Minimum Euclidean Distance Measure (MEDM) are introduced to optimize the matching process by minimizing differences between matched subjects. Understanding these methods is crucial for improving study validity and ensuring more accurate estimation of exposure-disease associations.