Pulmonary structures provide morphological basis for the vital functions to our body, which needs adequate airway flow, respiratory dynamics, lung ventilation, gas exchange, and lung perfusion closely interlinked with one another. For the CT evaluation of these functions, three-dimensional lung volumetry using the density mask techniques, dual-energy CT techniques, and cine and four-dimensional CT techniques may be used. To provide accurate and reproducible answers to clinical questions, we should first understand sources of variation influencing the results of these pulmonary functional CT exams. Then, we should know basic concepts, imaging techniques, and clinical applications of pulmonary functional CT. In addition to pulmonary anatomic details, pulmonary functional CT gives us new insights into lung physiology and ultimately opens new avenues in functional lung imaging.