Glaucoma is a multifactorial optic neuropathy in which there is a characteristic acquired loss of retinal ganglion cells, at levels beyond normal age-related baseline loss, and corresponding atrophy of the optic nerve. Although asymptomatic in its earlier stages, the disease is nevertheless one of the leading global causes of irreversible blindness. Although elevated intraocular pressure (IOP) is one of the most important risk factors and lowering of IOP is the only proven treatment so far, the definition of glaucoma has evolved from a disease caused by increased IOP to one characterised by an IOP-sensitive, progressive optic neuropathy. In recent years, safer and better tolerated topical medications have been developed to control IOP more effectively, thereby limiting the need for surgery. New research has also noted the importance of diurnal IOP variation as a critical risk factor for progression of glaucomatous optic neuropathy (GON) and subsequent visual field loss. Moreover, new discoveries have further elucidated the basic pathophysiological and genetic mechanisms underlying the elevated levels of IOP, as well as the cellular mechanisms of GON. As our understanding of these complex pathways continues to improve, development opportunities for new therapeutic modalities will be enhanced.