Practical tools for diagnosis of asthma. The key changes in this section are consequent upon the new definition of asthma, and are aimed at reducing both under- and over-diagnosis. There is an emphasis on making a diagnosis in patients presenting with respiratory symptoms, preferably before commencing treatment, and on documenting the basis of the diagnosis in the patient’s medical records. The chapter includes a table of specific criteria for documenting variable expiratory airflow limitation, a key component of asthma diagnosis, for use in clinical practice or clinical research. Other tests used in diagnosis of asthma are described in the report and appendix, with a reminder that statements in the literature about the sensitivity and specificity of “diagnostic” tools must be interpreted in the light of the definition of asthma that was used and the population that was studied; many studies, particularly those in which physician diagnosis was the gold standard, have primarily included patients with a classical allergic asthma phenotype. A list of common asthma phenotypes is provided, to prompt clinicians, including those in primary care, to recognise different clinical patterns among their patients, even if they lack access to complex investigations.