The pathological concept of obstructive lung diseases, including asthma and chronic obstructive pulmonary disease (COPD), has been formed by repeated integration and separation. Ten years have passed since the Global Initiative for Chronic Obstructive Lung Disease (GOLD) Guidelines were first published, in which COPD was comprehensively defined as a disease state characterized by airflow limitation that is not fully reversible. The heterogeneity of COPD is now being reemphasized, and classification into phenotypes has been promoted to lend it support. At the same time, because of the ambiguous boundaries among diseases encompassed by the pathological concept of COPD, there obviously exist patients with overlap syndromes between COPD and other lung diseases such as asthma and pulmonary fibrosis, which may be difficult to distinguish from COPD. The methods for clinical evaluation of COPD have also changed with changes in the pathological concept of this entity. More specifically, the need for multidimensional and comprehensive methods to evaluate the symptoms, frequency of exacerbations, and complications has been emphasized, instead of the one-dimensional standard severity assessment based on FEV₁ (forced expiratory volume in 1 s). The trend in treatment for COPD is now shifting from evidence-based medicine, which relies on randomized controlled studies, to stratified medicine for each phenotype. As a practice of the latter, inhaled corticosteroid therapy is recommended for patients with overlap syndromes with asthma or frequent exacerbations; however, the use of different treatment drugs are expected to be recommended for other phenotypes in the future. At present, next-generation comprehensive studies focusing on the genotypes and endotypes of COPD are being carried out, and an idea of systems medicine to understand the pathology and individual variations by organically integrating the enormous analysis results is being introduced. Whether personalized medicine, such as molecular target drugs for cancer, will be realized for COPD is unclear; however, considering the heterogeneity of COPD, we speculate that drugs effective for every COPD phenotype will be developed in the future in place of medications currently prescribed for all patients with COPD.