Red eye is the cardinal sign of ocular inflammation. The condition is usually benign and can be managed by primary care physicians. Conjunctivitis is the most common cause of red eye. Other common causes include blepharitis, corneal abrasion, foreign body, subconjunctival hemorrhage, keratitis, iritis, glaucoma, chemical burn, and scleritis. Signs and symptoms of red eye include eye discharge, redness, pain, photophobia, itching, and visual changes. Generally, viral and bacterial conjunctivitis are self-limiting conditions, and serious complications are rare. Because there is no specific diagnostic test to differentiate viral from bacterial conjunctivitis, most cases are treated using broad-spectrum antibiotics. Allergies or irritants also may cause conjunctivitis. The cause of red eye can be diagnosed through a detailed patient history and careful eye examination, and treatment is based on the underlying etiology. Recognizing the need for emergent referral to an ophthalmologist is key in the primary care management of red eye. Referral is necessary when severe pain is not relieved with topical anesthetics; topical steroids are needed; or the patient has vision loss, copious purulent discharge, corneal involvement, traumatic eye injury, recent ocular surgery, distorted pupil, herpes infection, or recurrent infections.