Primary open-angle glaucoma (POAG) affects 33 million individuals worldwide and is a leading cause of blindness. In a study of 54 families with autosomal dominantly inherited adult-onset POAG, we identified the causative gene on chromosome 10p14 and designated it OPTN (for "optineurin"). Sequence alterations in OPTN were found in 16.7% of families with hereditary POAG, including individuals with normal intraocular pressure. The OPTN gene codes for a conserved 66-kilodalton protein of unknown function that has been implicated in the tumor necrosis factor-alpha signaling pathway and that interacts with diverse proteins including Huntingtin, Ras-associated protein RAB8, and transcription factor IIIA. Optineurin is expressed in trabecular meshwork, nonpigmented ciliary epithelium, retina, and brain, and we speculate that it plays a neuroprotective role.