Type 2 inflammation in the airways and lungs is inflammation induced by type 2 cytokines such as IL-4, IL-5, and IL-13, produced primarily by type 2 helper T cells and type 2 innate lymphoid cells, and causes changes in the physiology and structure of the airways. Type 2 inflammation is currently in the spotlight because of its direct link to the treatment of several airway and lung diseases. Abundant evidences have accumulated that inflammatory biomarkers such as blood eosinophils, fractional exhaled nitric oxide, and IgE are essential clinical tools in the diagnosis and management of asthma and COPD. It is well known that asthma and COPD have diverse inflammatory phenotypes even when clinical features are similar, and it has been demonstrated that assessment of airway inflammation with biomarkers can improve diagnostic accuracy, determine safer and more effective treatment strategies, and predict future risks such as exacerbations and lung function decline. The Japanese Respiratory Society has published clinical practice guidelines for the evaluation of type 2 inflammation in the airways and lungs. In addition to asthma and COPD, the guide covers a wide range of airway and lung diseases, including interstitial lung disease, allergic bronchopulmonary mycosis, allergic rhinitis, and eosinophilic chronic rhinosinusitis. It also provides comprehensive guidelines covering a variety of clinical biomarkers. The purpose of this guidance is to provide evidences for the interpretation of type 2 inflammation measurements and to promote the widespread use of inflammation assessment to further improve the efficiency of airway and respiratory disease management.