This introductory chapter presents some basic information about tobacco and nicotine products, procedures for smoke collection (FTC, ISO, HCI), a general discussion about the chemical composition of tobacco, tobacco smoke, e-liquids and aerosols from ENDS, discusses the list of harmful and potential harmful compounds (HPHCs) as indicated by the US FDA, and presents several reference cigarettes and tobacco products as generated by Kentucky Tobacco Research & Development Center of the University of Kentucky. It also includes a short presentation of method validation in analytical chemistry. A short discussion about the role of analyses of toxicants played in the effort to reduce the danger of tobacco and nicotine use is also included.