O‐linked‐β‐N‐acetylglucosamine (O‐GlcNAcylation) is a distinctive posttranslational protein modification involving the coordinated action of O‐GlcNAc transferase and O‐GlcNAcase, primarily targeting serine or threonine residues in various proteins. This modification impacts protein functionality, influencing stability, protein–protein interactions, and localization. Its interaction with other modifications such as phosphorylation and ubiquitination is becoming increasingly evident. Dysregulation of O‐GlcNAcylation is associated with numerous human diseases, including diabetes, nervous system degeneration, and cancers. This review extensively explores the regulatory mechanisms of O‐GlcNAcylation, its effects on cellular physiology, and its role in the pathogenesis of diseases. It examines the implications of aberrant O‐GlcNAcylation in diabetes and tumorigenesis, highlighting novel insights into its potential role in cardiovascular diseases. The review also discusses the interplay of O‐GlcNAcylation with other protein modifications and its impact on cell growth and metabolism. By synthesizing current research, this review elucidates the multifaceted roles of O‐GlcNAcylation, providing a comprehensive reference for future studies. It underscores the potential of targeting the O‐GlcNAcylation cycle in developing novel therapeutic strategies for various pathologies.