Sublingual immunotherapy (SLIT) is accepted in the official documents and is currently used in many European countries. In recent years, new clinical data on efficacy and safety have been published, including meta-analyses in adults and children and surveys of safety in children younger than age 5 years. Moreover, it has been shown that, similar to the injection route, SLIT can prevent the onset of new sensitizations and the onset of asthma. Additionally, the mechanisms of action are beginning to be systematically studied. Some points need further investigation, such as the effect in asthma, the mechanisms of action, and the optimal dose to be administered.