Thioredoxin (TRX) is a highly conserved redox-regulatory protein that plays a crucial role in maintaining cellular redox homeostasis and modulating various cellular processes. The TRX system, which includes TRX, thioredoxin reductase (TRXR), and NADPH, acts as an essential antioxidant defense mechanism against oxidative stress by reducing oxidized proteins and neutralizing reactive oxygen species (ROS). TRX exists in multiple isoforms, such as cytosolic TRX1, mitochondrial TRX2, and spermatozoa TRX, with TRX1 being the most prominent and widely studied. It functions through its redox-active site (CGPC), which can reduce disulfide bonds in target proteins and transfer electrons to peroxiredoxins to eliminate oxidative stress. TRX also regulates gene expression, DNA synthesis, cell proliferation, and apoptosis, and has been implicated in various diseases, including cancer, neurodegenerative disorders, and cardiovascular diseases. Additionally, TRX can be secreted into the extracellular space under oxidative stress, acting as a chemotactic factor for immune cells and serving as a marker of oxidative stress.