Allergic conjunctivitis is a group of diseases that are frequent in childhood, associated to several allergic diseases affecting the ocular surface. It is related to type 1 hypersensitivity reactions. Two acute disorders: seasonal allergic conjunctivitis and perennial allergic conjunctivitis, exist, as do three chronic diseases: vernal keratoconjunctivitis, atopic keratoconjunctivitis and giant papillary conjunctivitis. The ocular surface inflammation causes itching, tearing, lid and conjunctival edema-redness, and photophobia during the acute phase and can lead to a classic late-phase response (associated to eosinophilia and neutrophilia) in a subset of individuals. As in the case of several chronic allergic diseases, it can remodel the ocular surface tissue. This allergic disease is very frequent. Vernal keratoconjunctivitis could produce corneal lesions and visual illness; however, atopic keratoconjunctivitis does not permanently affect the vision. The aim of this review is to provide a current overview for a better understanding of the symptoms associated to this disease, to describe its classification, recent advances in its physiopathology and its treatment.