T-cell Immunoglobulin and Mucin-Domain-Containing Molecule-3 (TIM3), also called Hepatitis A virus cellular receptor 2, HAVCR2, is present on T-helper type 1 lymphocytes and other immune cells including dendritic cells and natural killer cells. TIM3 consists of an IgV-like domain, a mucin-like domain in the extracellular region, and a conserved Tyrosine phosphorylation motif in the cytoplasmic region. TIM3 is involved in macrophage activation and induction of autoimmune diseases. Further, TIM3 down-regulates aggressive Th1-mediated immune responses and facilitates in the development of immune tolerance. TIM3 is overexpressed in CD4+ tumor-infiltrating lymphocytes, including those with non-small cell lung cancer associated with poor prognoses. TIM3 has recently emerged as a potential target for cancer immunotherapy.