Allergic rhinitis (AR) affects more than 20% of the population in the United Kingdom and western Europe and represents a major cause of morbidity that includes interference with usual daily activities and impairment of sleep quality. This guidance prepared by the Standards of Care Committee (SOCC) of the British Society for Allergy and Clinical Immunology (BSACI) is for the management of AR in patients that have failed to achieve adequate relief of symptoms despite treatment with intranasal corticosteroids and/or antihistamines. The guideline is based on evidence and is for use by both adult physicians and paediatricians practising allergy. During the development of these guidelines, all BSACI members were included in the consultation process using a web-based system. Their comments and suggestions were carefully considered by the SOCC. Where evidence was lacking, consensus was reached by the experts on the committee. Included in this guideline are indications and contraindications for immunotherapy, criteria for patient selection, the evidence for short- and long-term efficacy of subcutaneous and sublingual immunotherapy, and discussion on safety and the different modes of immunotherapy including, pre-seasonal and co-seasonal treatments. There are sections on children, allergen standardization, vaccines used in the United Kingdom, oral allergy syndrome, cost effectiveness of immunotherapy and practical considerations of undertaking immunotherapy including recommendations on who should undertake immunotherapy and dosing schedules. Finally, there is discussion on potential biomarkers of response to immunotherapy, the use of component-resolved diagnostics, novel approaches, alternative routes and potential areas for future research.