Ocular allergic disease affects not only the conjunctivae but also surrounding structures including the eyelids. Allergic diseases of the eyelid include atopic dermatitis, contact dermatitis, and urticaria/angioedema. They must be differentiated from nonallergic eyelid diseases. Allergic diseases of the conjunctivae comprise a spectrum of disorders from common, non-sight-threatening conditions such as seasonal allergic conjunctivitis, perennial allergic conjunctivitis, and giant papillary conjunctivitis to less common and potentially sight-threatening diseases such as vernal keratoconjunctivitis and atopic keratoconjunctivitis. Each of these conditions is mediated primarily by type I hypersensitivity reactions. The clinical manifestations, differential diagnosis, and treatment of these conditions are reviewed in this article.