Optic disc edema is the end result of many pathological processes, some relatively benign, some with devastating visual and neurological consequences. Differentiating among the various etiologies depends on a thorough history and complete examination with careful attention to the optic disc. Papilledema implies disc swelling due to elevated intracranial pressure, and can be distinguished from other causes of disc edema by clinical features. Congenitally anomalous optic discs may appear swollen, and proper recognition may spare patients unnecessary testing. The pathogenesis of disc swelling remains subject to debate, but the ultimate mechanism is backflow of axoplasmic transport. The treatment strategy for disc edema highly depends on the underlying etiology.