In the framework of evidence-based medicine, quantitative biomarkers are needed to adequately diagnose disease, predict prognosis, and assess the effects of therapy. Among others, respiratory conditions such as COPD or asthma are common chronic diseases that place an important burden on healthcare costs. Reliable measurements of respiratory parameters that are altered in these diseases could contribute to standardizing and rationalizing their management and potentially decreasing the associated expenses. Quantitative measurements of lung volumes, emphysema, and air trapping are now achievable in routine practice through imaging. The aim of this chapter is to review the pathophysiological basis of these respiratory parameters, the principles on which their measurements rely, the technical requirements for adequate quantitative assessments, and the interpretation of the measurement results.