Specific Immunotherapy for respiratory allergy is used since about one century and there is now solid documentation of its efficacy. Nevertheless, the methods and experimental designs used in clinical trials are quite heterogeneous and there is no unanimously accepted methodological standard. Many studies are planned with study designs that may not confirm the clinical value of SIT as an effective treatment to reduce disease severity. To ensure that patients are treated based on sound scientific evidence and to minimize the risk of misusing limited financial resources for scientific studies, the World Allergy Organization (WAO) convened a group of experts to provide guidelines for the methodology of future immunotherapy studies. This document summarizes the recommendations for study design, patients' selection, appropriate outcomes and statistical treatment to be used in planning and performing clinical trials with specific immunotherapy.