Phlyctenular keratoconjunctivitis (PKC) is a delayed type hypersensitivity reaction characterized by subepithelial nodules seen in the conjunctiva, limbus, and cornea, in response to an inciting antigenic factor. The most common source of PKC is a hypersensitivity reaction to tuberculoprotein and other causative agents include Myobacterium tuberculosis, Staphylococcus aureus, Propionibacterium acnes, parasitic infection, fungal infection, and HLA subtypes A26, B35, and DR8. PKC is not a blinding disease but it is a source of lowered visual acuity and a noninfectious inflammatory condition. This chapter gives a comprehensive review of the clinical manifestations, pathophysiology, etiology, and management of PKC. Symptoms of PKC include blurry vision, irritation, lacrimation, photophobia, and injection. Phlyctenulosis may also be an incidental finding in asymptomatic patients with a recent history of bacterial, parasitic, or fungal infection and phlyctenular conjunctivitis may occur in the absence of a keratitis also. Diagnosis is largely by history and clinical presentation. Treatment methods include antimicrobial and anti-inflammatory agents.