Allergic conjunctivitis is the most common manifestation of conjunctivitis, affecting up to 40% of the population, mostly children and young adults. Among the risk factors there are air pollution, southern latitude and coexisting allergy. The disease develops when IgE-class antibodies are activated by an allergen and later Th2-dependent humoral response is activated. In seasonal and perennial allergic conjunctivitis the symptoms are limited to conjunctiva, however in vernal keratoconjunctivitis and atopic keratoconjunctivitis also the cornea can be affected. Giant papillary conjunctivitis is not an allergy but a response to irritating surface agents, most frequently a contact lens. In treatment there are three groups of medications used: antihistaminic, non-steroid anti inflammatory and steroids. Due to rise of allergic conjunctivitis, it is crucial to accurately diagnose and treat those conditions.