This monograph presents a series of review studies linking tobacco smoke and involuntary (passive) smoking to several cancers. Evidence of synergy between smoking and several occupational causes of lung cancer (arsenic, asbestos, and radon) and between smoking and alcohol consumption for cancers of the oral cavity, pharynx, larynx, and oesophagus and between smoking and human papillomavirus infection for cancer of the cervix have been found. In addition, the working group concluded that involuntary smoking (exposure to secondhand or environmental tobacco smoke) is carcinogenic to humans.