Stage classification provides a nomenclature about the anatomic extent of a cancer; a consistent language provides the ability to communicate about a specific patient and about cohorts of patients in clinical studies. This paper summarizes the eighth edition of lung cancer stage classification, which is the worldwide standard as of January 1, 2017. This revision is based on a large global database, a sophisticated analysis, extensive internal validation as well as multiple assessments confirming generalizability. Practicing clinicians must be familiar with the stage classification system when managing contemporary patients with lung cancer.