Glaucoma is a neurodegenerative disease and one of the leading causes of irreversible blindness, affecting over 60 million people worldwide. At the present time, glaucoma is clinically defined, but the exact etiology is unknown. Genetic studies are one approach to identify the molecules and pathways involved in disease pathogenesis. Familial aggregation of primary open-angle glaucoma (POAG) has long been recognized, and the analysis of POAG families with a Mendelian inheritance form of this disease has been employed to identify multiple loci linked to them. Some causative genes, such as myocilin, optineurin and WD repeat domain 36, have been identified. However, most cases of POAG are considered to be a prevalent, multifactorial disorder. Several association studies have been conducted for candidate genes, and genome-wide association studies recently identified new susceptibility loci for POAG, namely, S1 RNA binding domain 1 region on chromosome 2p21, the caveolin 1 and caveolin 2 regions on 7q31, transmembrane and coiled-coil domain 1 region on 1q24, cyclin-dependent kinase inhibitor 2B antisense RNA on 9p21, the SIX1 and SIX6 regions on 14q24 and, possibly, the regulatory region of 8q22. Further analysis of clinical manifestations caused by specific genes and functional analysis of these genes will contribute to the development of new strategies for the diagnosis and treatment of POAG.