The term glaucoma describes a heterogeneous group of optic neuropathies that lead to optic nerve atrophy and permanent loss of vision. It is the second most prevalent cause of bilateral blindness in the Western world and affects over 60 million people worldwide. The hereditary forms of glaucoma are genetically heterogeneous. Different forms of glaucoma can be distinguished: the primary open-angle glaucoma of adult onset is the most common, representing approximately half of all cases. The juvenile-onset open-angle glaucoma is an uncommon autosomal dominant form of glaucoma with manifestation predominantly before the fourth decade of life. The primary congenital glaucoma is a clinical and genetic entity clearly distinct from the juvenile form, following an autosomal recessive mode of inheritance. At least eight loci have been linked to glaucoma (GLC1A-F, GLC3A/B) and three genes have been identified to date: MYOC, CYP1B1 and OPTN. In the last decade, there has been much progress in finding new genes, detecting disease-related mutations and determining allele frequencies within populations of different ethnical backgrounds, but little is known about the function of the mutated gene products and the underlying pathogenic mechanisms. This chapter attempts to summarize the current knowledge regarding glaucoma-associated genes.