This issue of Immunology and Allergy Clinics provides a comprehensive review of the current state of biomarkers and their role in the asthma diagnostic and therapeutic algorithm.Since the last issue on Biomarkers, which published in 2007, significant research directly targeted at biomarker development and clinical trials with new biologics, using biomarkers such as exhaled nitric oxide, sputum and tissue eosinophilia as endpoints, has occurred.