Lung cancer is the leading cause of cancer-related death in the United States, with an average five-year survival rate of 15 percent. Smoking remains the predominant risk factor for lung cancer. Lung cancers are categorized as small cell carcinoma or non-small cell carcinoma (e.g., adenocarcinoma, squamous cell carcinoma, large cell carcinoma). These categories are used for treatment decisions and determining prognosis. Signs and symptoms may vary depending on tumor type and extent of metastases. The diagnostic evaluation of patients with suspected lung cancer includes tissue diagnosis; a complete staging work-up, including evaluation of metastases; and a functional patient evaluation. Histologic diagnosis may be obtained with sputum cytology, thoracentesis, accessible lymph node biopsy, bronchoscopy, transthoracic needle aspiration, video-assisted thoracoscopy, or thoracotomy. Initial evaluation for metastatic disease relies on patient history and physical examination, laboratory tests, chest computed tomography, positron emission tomography, and tissue confirmation of mediastinal involvement. Further evaluation for metastases depends on the clinical presentation. Treatment and prognosis are closely tied to the type and stage of the tumor identified. For stages I through IIIA non-small cell carcinoma, surgical resection is preferred. Advanced non-small cell carcinoma is treated with a multimodality approach that may include radiotherapy, chemotherapy, and palliative care. Chemotherapy (combined with radiotherapy for limited disease) is the mainstay of treatment for small cell carcinoma. No major organization recommends screening for early detection of lung cancer, although screening has interested researchers and physicians. Smoking cessation remains the critical component of preventive primary care.