The new World Health Organization (WHO) classification of lung tumors, developed in collaboration with the International Association for the Study of Lung Cancer (IASLC), aims to improve reproducibility, clinical significance, and simplicity. Key changes include the addition of two pre-invasive lesions—atypical adenomatous hyperplasia and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia—and the reclassification of adenocarcinoma. The definition of bronchioloalveolar carcinoma (BAC) has been restricted to noninvasive tumors, and the large cell neuroendocrine carcinoma (LCNEC) and basaloid carcinoma have been recognized as distinct variants with poor prognosis. The classification also includes a new category for carcinomas with pleomorphic, sarcomatoid, or sarcomatous elements. Immunohistochemistry and electron microscopy are valuable for diagnosis and subclassification but are not essential for routine use. Molecular studies have provided deeper insights into the biology of lung tumors, particularly in understanding the neoplastic nature of certain lesions. The classification is designed to be widely applicable, even in surgical pathology laboratories without advanced techniques.The new World Health Organization (WHO) classification of lung tumors, developed in collaboration with the International Association for the Study of Lung Cancer (IASLC), aims to improve reproducibility, clinical significance, and simplicity. Key changes include the addition of two pre-invasive lesions—atypical adenomatous hyperplasia and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia—and the reclassification of adenocarcinoma. The definition of bronchioloalveolar carcinoma (BAC) has been restricted to noninvasive tumors, and the large cell neuroendocrine carcinoma (LCNEC) and basaloid carcinoma have been recognized as distinct variants with poor prognosis. The classification also includes a new category for carcinomas with pleomorphic, sarcomatoid, or sarcomatous elements. Immunohistochemistry and electron microscopy are valuable for diagnosis and subclassification but are not essential for routine use. Molecular studies have provided deeper insights into the biology of lung tumors, particularly in understanding the neoplastic nature of certain lesions. The classification is designed to be widely applicable, even in surgical pathology laboratories without advanced techniques.