Migraine aura consists of fully reversible focal neurologic symptoms that may precede or coexist with headache in a significant minority of migraine patients. Typical aura symptoms include visual, sensory, and language disturbances. The most recent International Classification of Headache Disorders, 3rd edition (beta version) has added other aura types such as brainstem localizing symptoms, lateralizing weakness, and monocular visual loss. Currently available data from animal models and functional neuroimaging in humans implicate cortical spreading depression (CSD) as the phenomenon underlying migraine aura. Ongoing study suggests that susceptibility to migraine aura and CSD may be genetically mediated. CSD appears to be a potential target for future development of migraine-specific preventive therapies.