Galectin-9 is a member of the lectin family, which includes 15 mammalian lectin members. Like all galectins, Galectin-9 contains a carbohydrate recognition binding domain that enables specific binding of β-galactosides. Most galectins are either bivalent or multivalent in regards to their carbobydrate binding capacity, which enables the recognition of distinct signalling pathways. Galectin-9 may be retained intracellularly or transported to the cell surface where it can be cleaved to generate a soluble form. Galectin-9 functions in effector and regulatory phases of the immune response. During inflammation, the production of Galectin-9 in vivo generates a microenvironment that limits effector T cell responses. Galectin-9 can negatively regulate the Th1 immune response by engaging TIM-3 on T cells, which leads to induction of intracellular Ca2+ influx and activation of apoptosis pathways. In addition, Galectin-9 has been shown to function as a urate transporter in the kidney. Galectin-9 has been identified as a possible prognostic marker in breast cancer, melanoma, and oral squamous cell carcinomas.