The International Association for the Study of Lung Cancer Retrospective Staging Project culminated in a series of recommendations to the International Union Against Cancer and to the American Joint Committee on Cancer regarding the seventh edition of the tumor, node, metastasis (TNM) classification for lung cancer. The International Staging Committee of the International Association for the Study of Lung Cancer now issues this call for participation in the Prospective Project designed to assess the validity of each component of T, N, and M, and other factors relevant to lung cancer staging and prognosis. In the Retrospective Project, the original data acquisition was typically motivated by interests other than staging. In contrast, the Prospective Project offers online data entry. Alternatively, participants may transfer existing data, provided core objectives are addressed. Cancer Research and Biostatistics will coordinate data management and analysis. The study population is newly diagnosed lung cancer patients. Data elements include patient characteristics, baseline laboratory values, first-line treatment, TNM plus supporting evidence, and survival. Pretreatment TNM will be collected for all cases; postsurgical TNM, if resection is attempted. T descriptors include size and degree of tumor extension, with further description of extent of visceral pleural invasion, venous invasion, carcinomatous lymphangitis, and pleural lavage cytology. M descriptors characterize the newly proposed M1a category and sites of distant metastases. Nodal station involvement is described by means of a newly proposed nodal map, facilitating international participation, and allowing further investigation of nodal zones. Successful collection and analysis of these data can be expected to yield unprecedented improvements in the utility and validity of lung cancer staging.