This technical report provides the evidence base for the accompanying tobacco clinical report and policy statement. It builds on, strengthens, and expands AAP recommendations from the previous version in 2015. Tobacco use remains the leading preventable cause of disease and death for adults in the United States. The tobacco epidemic takes a substantial toll on children's and adolescent's health, including harms because of prenatal exposure during pregnancy, secondhand and thirdhand exposure during infancy and childhood, and/or direct use during adolescence. Tobacco and nicotine use almost always starts in childhood or adolescence. Almost 40% of children aged 3 to 11 years are regularly exposed to secondhand tobacco smoke, and rates of secondhand exposure to e-cigarette aerosol have increased over the last decade.