Nowadays, over 80 000 specific sites with PTMs have been discovered, including acetylation, phosphorylation, glycosylation, methylation, and ubiquitination. O-GlcNAcylation is a special case of O-linked glycosylation, which is a reversible post-translational modification that regulates the function of numerous cytosolic and nuclear proteins depending on the energy, nutrition and stress status of the cell. O-GlcNAcylation is involved in many biological processes, like transcription, translation, metabolism, signal transduction, embryogenesis, and epigenetics. In this work, my objective was to review the main characteristics of this PTM focusing on the O-GlcNAcylation pathway itself, the enzymes catalyzing the process, the connected diseases, and its role in the biology of eukaryotes.