The terms organizing pneumonia and cryptogenic organizing pneumonia are sometimes used for the broad category of patients with organizing pneumonia. There are several reasons that the term BOOP should continue to be used for the clinical disorder and corresponding pathological lesion described in this review. First, investigators and clinicians throughout the world recognize the clinical and pathological features of this disorder, and they commonly use the term BOOP. Second, BOOP is a histological process that involves distal airways and alveoli simultaneously. Although various lung diseases represent a chronic inflammatory process, it is now apparent that the processes differ markedly among various diseases, such as chronic obstructive pulmonary disease, asthma, and BOOP, with different inflammatory cells, mediators, inflammatory effects, and response to treatment.8 Therefore, an inflammatory lesion that involves only airways or only alveoli may have different inflammatory components than the BOOP lesion that involves airway and alveoli simultaneously. Third, investigations of specific treatments for BOOP will be more strongly positive if the specific definition of BOOP is used for inclusion of patients rather than using the broad definition of organizing pneumonia. This is similar to IPF, in which many distinct histological disorders were included in this category in the past, resulting in dilution of the actual mechanism and poor treatment results. Now that IPF is limited to UIP,3 the opportunity to fully characterize the fibrotic pathway is much greater, and antifibrotic treatment tailored to this fibrotic pathway will be tested more efficiently and accurately.