Lung cancer remains the leading cause of cancer-related mortality in the United States despite a decades-long decline in incidence resulting from a decrease in tobacco use and the implementation of widespread screening in high-risk patients. Lung cancer is classified based on the cell type of origin, such as from the tissues lining the airways (bronchogenic) or the connective tissues (mesenchymal) and based on the histology of these tissues (small cell and non-small cell carcinoma). The World Health Organization (WHO) classification further subdivides non-small cell histology into adenocarcinoma, squamous cell, and large cell carcinomas. All lung cancer is staged based on the IASLC tumor, nodal, and metastasis (TNM) system, which informs the AJCC system and incorporates the size and extent of invasion of the tumor (T), the amount and location (or station) of lymph nodes involved by the cancer (N), and the presence and location of distant metastatic disease (M). Treatment planning is dependent on a histologic diagnosis, TNM tumor staging, and the results of molecular diagnostic studies that may highlight gene mutations with available therapeutics.