This text consists of neoplastic and non-neoplastic lung pathology. It discusses frequently encountered issues and diagnostic problems using a Q&A format and case presentations.  Emphasis is placed on differentiating one from another based on the histopathological features, ancillary tests including immunohistochemical and molecular analyses, and clinical and radiologic correlation. In particular, clinical-radiologic-pathologic correlation is emphasized in the diagnosis of interstitial lung disease (ILD).     This text addresses the issues and diagnostic criteria in segregating a reactive process from adenocarcinoma, poorly differentiated adenocarcinoma from poorly differentiated squamous cell carcinoma, small cell carcinoma from other types of neuroendocrine tumors, large cell carcinoma from large cell neuroendocrine carcinoma, spindle cell/sarcomatoid carcinoma from sarcomatoid mesothelioma, and carcinoma from epithelioidmesothelioma in small biopsy specimens. It also discusses key features useful for differentiating usual interstitial pneumonia (UIP) pattern from non-UIP patterns of ILD such as hypersensitivity pneumonitis, nonspecific interstitial pneumonia, and organizing pneumonia patterns in wedge biopsy specimens as well as highlights the differential diagnosis in the granulomatous inflammation.   As a whole, this text answers many of the difficult questions relevant to daily practice of lung pathology. Each chapter addresses a specific diagnostic question significantly related to patients' treatment options.