Pathophysiological assessment is important for the management of chronic obstructive pulmonary disease (COPD). The assessment method has changed over the 14 years during which the first to the fourth editions of COPD guidelines were published by the Japanese Respiratory Society. In the first edition, only %FEV1 was an index for the pathological assessment, and in the second edition, the presence or absence of respiratory failure was added. In the third edition, because %FEV1 has not be shown to assess COPD severity fully, dyspnea, exercise capacity, and exacerbation frequency were added for the pathophysiological assessment. The fourth edition was published last year, and in this new edition physical activities are applied for the pathophysiological assessment with the items that have been provided in the third edition. Also added are the disease types by HRCT, general comorbidity, and pulmonary complications.