Human interferon-gamma (IFN-γ) is a dimeric cytokine with subunits of 146 amino acids. Mature human IFN-γ exists as a non-covalently linked homodimer of 20-25 kDa variably glycosylated subunits. IFN-γ does not display significant homology with the other two interferons, IFN-alpha and IFN-beta. Murine and human IFN-γ show approximately 40% sequence homology at the protein level. IFN-γ is expressed by Th1 cells, Tc cells, dendritic cells and natural killer cells, especially under inflammation conditions. IFN-γ binds to its heterodimeric receptor IFN-γR and related complex for biological function. It plays a key role in host defense by promoting the development and activation of Th1 cells, chemoattraction and activation of monocytes and macrophages, upregulation of antigen presentation molecules, and immunoglobulin class switching in B cells. In addition, IFN-γ functions as an anti-inflammatory mediator by promoting the development of regulatory T cells and inhibiting Th17 cell differentiation. It also exhibits antiviral, antiproliferative, and apoptotic effects. IFN-γ is also an attractive drug target for immuno-regulatory diseases.