Chronic progressive external ophthalmoplegia (CPEO) is a descriptive term for a heterogenous group of disorders characterized by chronic, progressive, bilateral, and usually symmetric ocular motility deficit and ptosis. Significant pain, proptosis, or pupil involvement are not features of CPEO and should prompt evaluation for alternative etiologies. Mitochondrial DNA mutations are increasingly being recognized as the etiology for CPEO syndromes. Clinicians should recognize the specific syndromes associated with CPEO, characterized by variable systemic, neurologic, or other findings. Treatment is limited, but newer therapies are being investigated.