An overview how to examine pupillary function and handle pupillary abnormalities is presented. The following issues are discussed: swinging flashlight test, clinical relevance of a relative afferent pupillary defect, anisocoria with normal light reaction, diagnosis and evaluation of Homer's syndrome, differential diagnosis of impaired light reaction, tonic pupil, third nerve palsy, supranuclear pupillary disorders, iris problems, systemic disease, measurement of sleepiness, and pupillography.