The leading cause of lung cancer is exposure to cigarette smoke and other environmental pollutants, which include formaldehyde, acrolein, benzene, dioxin, and polycyclic aromatic hydrocarbons (PAHs). PAHs and dioxins are exogenous ligands that directly bind to the aryl hydrocarbon receptor (AhR), a transcription factor that activates xenobiotic metabolism, histone modification (an important step in DNA methylation) and, ultimately, tumorigenesis. In this review article we summarize the current understanding of AhR and its role in the development of lung cancer, including its influence on cell proliferation, angiogenesis, inflammation, and apoptosis.