Numerous controlled clinical trials have demonstrated the efficacy of specific allergen immunotherapy (SIT) in reducing the clinical symptoms and costs associated with allergic rhinitis. Compared with pharmacotherapy, SIT may provide persistent clinical benefits after treatment discontinuation. Subcutaneous and sublingual immunotherapy are the two most widely prescribed SIT routes worldwide. This review compares the efficacy, safety, preventive effect, immunologic mechanisms, and adherence rates associated with these two forms of SIT.