The electrical activity generated by retinal ganglion cells (RGCs) and their axons is recordable with different ERG modalities, among which the Pattern ERG (PERG) in response to contrast-reversing patterns is the best known and understood. The PERG reflects the spatial, temporal, and chromatic properties of RGCs and it is readily recordable in human and experimental animals with high signal-to-noise ratio. The PERG is altered when RGCs are either degenerated or still alive but dysfunctional. In glaucoma, PERG loss may be reversible after treatment after IOP-lowering treatment. Progressive PERG loss in glaucoma-prone subjects precedes loss of retinal nerve fiber layer thickness by several years, and PERG progression may be hindered after IOP lowering. PERG loss may be inducible in susceptible eyes of glaucoma suspects upon head-down posture, which may predict future RGC loss. PERG provides unique information, complementary to OCT imaging and Visual Field, which may help in glaucoma diagnosis and management. The presence of comorbidities such as cataract ad diabetes may nonspecifically alter the PERG.