S-Glutathionylation is a post-translational modification process by which the antioxidant molecule glutathione (GSH) is covalently attached to cysteine residues in proteins, forming mixed disulfides. This process is dynamic and reversible, and it is involved in the modulation of a wide range of cellular processes, such as redox signaling, protein synthesis and degradation, metabolic pathways, and apoptosis. The S-glutathionylation process is regulated by the enzymes glutaredoxin and glutathione-S-transferase, which catalyze the transfer and removal of glutathione from cysteine residues, respectively. The level of S-glutathionylation is also influenced by the redox status of the cell, as the production of reactive oxygen species (ROS) can lead to the formation of oxidized glutathione (GSSG), which in turn promotes S-glutathionylation. Many proteins are known to undergo S-glutathionylation, including enzymes, transcription factors, and cytoskeletal proteins, among others. Some of the best characterized targets of S-glutathionylation are the redox-sensitive cysteine residues of proteins involved in signaling pathways, such as protein tyrosine phosphatases (PTPs) and protein kinases (PKs). S-glutathionylation of PTPs, which are negative regulators of signaling pathways, can lead to their inactivation and potentiation of downstream signaling. On the other hand, S-glutathionylation of PKs, which are positive regulators of signaling pathways, can lead to their activation and promotion of downstream signaling. The S-glutathionylation process is also involved in the regulation of oxidative stress and cellular homeostasis. As GSH is a potent antioxidant, S-glutathionylation can protect cysteine residues from irreversible oxidation by ROS. Moreover, S-glutathionylation can facilitate the removal of damaged or misfolded proteins through the ubiquitin-proteasome system (UPS), by tagging them for degradation. In summary, the S-glutathionylation process is a versatile post-translational modification that is involved in the regulation of multiple cellular processes, including redox signaling, protein synthesis and degradation, and apoptosis. Its dynamic and reversible nature, as well as its dependence on the redox status of the cell, make it a key player in the maintenance of cellular homeostasis.