Human leukocyte antigen (HLA) gene region encodes a set of HLA molecules functioning critical roles in immune response. Each HLA gene locus shows extensive polymorphism with ever-increasing number of alleles. The HLA nomenclature system for alleles defined by DNA typing was first established in 1987 and has been revised several times. Recently, it has been revised again with a new frame that can accommodate ever-increasing number of new alleles. The new system has also introduced the novel suffixes, P and G, to simplify reporting of ambiguous strings of alleles in typing reports. This review introduces the HLA nomenclature system-2010 in conjunction with its clinical application in Koreans.