PD-L1, also known as B7-H1 and CD274, is a 290 amino acid transmembrane glycoprotein in the B7 family of immune regulatory molecules. It has an extracellular domain that can interact with PD-1, which belongs to the CD28/CTLA4 family expressed on activated lymphoid cells. The PD1/PD-L1 interaction ensures that activation of the immune system occurs at the appropriate time. This will minimize the possibility of chronic autoimmune inflammation. PD-L1 is known to inhibit proliferation of T cells via apoptosis. It also plays an important role in arresting cell-cycle progression. This makes PD-L1 an attractive therapeutic target for cancer and immunologic diseases.