Sublingual immunotherapy (SLIT) has been shown to be safe and efficacious in treating allergic rhinitis. It has been used in Europe for more than 20 years, and interest in the United States is increasing. SLIT has been shown to elicit immunologic changes similar to subcutaneous injection immunotherapy. SLIT may prevent new sensitizations, improve asthma control, and decrease asthma development in allergic individuals. Although differences in antigen quantification and standardization make European dosing schemes difficult to translate in the United States, several new studies suggest the range for effective dosing. Further studies will help clarify optimal dosing.