The introduction of specific humanized monoclonal antibodies over the past 20 years has dramatically changed the treatment of allergic diseases. At present, five monoclonal antibodies are licensed for treating moderate to severe allergic and eosinophilic asthma, atopic dermatitis, chronic spontaneous urticaria, chronic sinusitis with nasal polyps, and eosinophilic granulomatosis with polyangiitis. Given the high costs of biologics, understanding their cost-effectiveness is critical. As new biologics are developed and new indications are approved for existing biologics, use of biologics for allergic diseases will increase. Conducting cost-effectiveness evaluations in parallel to efficacy and effectiveness trials will help patients, providers, payers, and policy makers in decision-making.