Allergic conjunctivitis (AC) includes a wide spectrum of clinical entities characterized by different incidence, age of onset, natural course, clinical outcome and response to treatment. Taken together, they represent one of the most frequent ocular surface diseases affecting more than 30% of the young-adult population and show an increasing incidence over the years. Moreover, comorbidities with other systemic atopic conditions such as asthma, atopic dermatitis and rhinitis require a multidisciplinary approach. Recent advances in the knowledge of the pathogenic mechanism overcome the classic role of type I hyper-sensitivity and mast cells activation, demonstrating an involvement of innate immunity and neuroinflammation in the pathogenesis of the most severe forms such as atopic keratoconjunctivitis (AKC) and vernal keratoconjunctivitis (VKC). Ocular itching, swelling and tearing are the most frequent symptoms complained by patients with all forms of AC, while photophobia and pain are typical of the most severe forms, such as VKC and AKC, due to the frequent corneal involvement. Upper tarsal papillary reaction represents the main clinical sign of AC associated with conjunctival hyperemia and mucous secretion. Diagnosis is based on clinical history and eye evaluation and can be confirmed through allergological tests. Additional ocular exams include specific allergen conjunctival provocation tests and the presence of eosinophils in the conjunctival scraping. Current treatments of AC include the use of antiallergic eye drops for mild forms, while recurrences of ocular surface inflammations with corneal involvement in severe forms require the use of topical steroids to avoid visual impairment. Novel steroid sparing therapies such as Cyclosporine A eye drops or topical Tacrolimus have been proposed to improve VKC and AKC management.