Gingival recession is a common finding in many patients and is clinically manifested by an apical displacement of the gingival margin in relation to the cemento-enamel junction (CEJ). Various classification systems have been proposed to classify gingival recession defects and to predict final root coverage outcomes. Among them, the Miller classification is still the most commonly used among dental practitioners and researchers. This chapter reviews the different classification systems available for gingival recession defects and explores the strengths and limitations of them.