Lung cancer is a significant contributor to cancer-related mortality both in the United States and globally, and both first- and second-hand exposure to tobacco smoke is the predominant risk factor for lung cancer. Lung cancer is classified as non-small cell lung cancer, small cell lung cancer, or mesothelioma. NSCLC is further classified by the histological subtypes of adenocarcinoma (more prevalent in people who have never smoked cigarettes) and squamous cell carcinoma (more prevalent in people with a cigarette smoking history). Small cell lung cancer is closely associated with current or former tobacco use. Mesothelioma is closely associated with occupational asbestos exposure, and smoke exposure has a synergistic effect. These environmental risk factors can contribute to the acquisition of acquired genetic and chronic inflammatory changes that, in addition to an inherited genetic susceptibility to cancer, promote the development (carcinogenesis) of cancer. These clear risk factors for lung cancer allow for the identification of certain high-risk populations that benefit the most from lung cancer screening, which has contributed to a reduced incidence of lung cancer. The current guidelines recommend low-dose CT for patients aged 50–80 who have a ≥20-pack-year smoking history and who currently smoke or have quit within the past 15 years.