Lung cancer is the most common fatal malignancy in the world and smoking is the main risk factor. The carcinogens in tobacco smoke induce complex genetic interactions within the entire bronchial tree, leading to field carcinogenesis and tumour development. There are many different types of lung cancer and classification is important because it guides management. Morphology and immunohistochemical techniques are used to type a tumour biopsy and subsequent treatment, including surgery in some cases, is initiated. Postoperatively, staging and definitive classification of the tumour is used to predict prognosis.