The patient with a tender, erythematous, swollen eyelid represents a complex clinical challenge to the physician, who must arrive at a correct diagnosis from numerous differential possibilities. Knowledge of the anatomy of the orbit and surrounding structures and proper clinical and radiologic examination are necessary to accurately diagnose these conditions. Proper selection of antibiotic therapy and timely surgical intervention, directed at both the orbital infection and the underlying condition, are essential to avoid serious morbidity from these infections. This article reviews in detail preseptal cellulitis, Hemophilus influenzae type B infection in children, orbital infection related to paranasal sinusitis, orbital infection from other causes, and mycotic infections of the orbit.