While the basic classification of lung cancer has not altered drastically over the course of the last several years, histologic criteria have undergone a slow, progressive evolution. Input from biological studies has aided the subtyping of some tumors, especially SCLC, and helped delineate the importance of the accurate typing of NSCLC. Newer technological advances, especially in molecular biology, and application of established immunohistochemical techniques using newly generated antibodies are beginning to impact on diagnosis and typing. The evolution and application of clinical protocols directed to specific types or subtypes of lung cancer will provide an even greater impetus to these studies.