Microbial keratitis is a sight-threatening infection of the cornea. Without timely treatment, it can lead to corneal perforation, endophthalmitis, and even loss of the eye. Even with treatment, scar resulting in permanent vision loss is common. The epidemiology of these cornea infections varies with geographic region, occupation, and socioeconomic status. Both intrinsic (e.g., ocular surface disease) and extrinsic (e.g., trauma) risk factors are reviewed. Infection may be caused by bacteria, viruses, fungi, or parasites. Pearls relevant to specific organisms are discussed, as are several diagnostic algorithms. The immediate goal of the clinician is to clear the infection and prevent the abovementioned complications. This is usually done medically with topical antimicrobial drops, but surgery is sometimes indicated. Later, after the infection has resolved, measures to restore vision may be applied. These include updated spectacle prescriptions, the use of rigid contact lenses, and cornea transplant surgery.