The word 'substance' can refer to a drug of abuse, a medication or a toxin. 'Polysubstance' Abuse/Dependence means that a person abuses or depends upon more than one substance, with one usually being that persons favourite or 'drug of choice'. It is important to note that we are not only referring to illegal drugs; over the counter or prescription drugs are often abused as well. The more commonly abused drugs today are cocaine, marijuana, inhalants and heroin. Substance exposure that can cause substance related disorders include heavy metals (e.g., lead, rat poison containing strychnine, certain pesticides, nerve gas, antifreeze, carbon dioxide and carbon monoxide). The medications, both prescriptive and over the counter, that may cause substance related disorders include anaesthetics, analgesics, anticonvulsants, antihistamines, blood pressure and heart medication and muscle relaxants. This important book presents state-of-the-art research in this field.