The use of licit or illicit substances during pregnancy has the potential to produce adverse health effects for the maternal-fetal dyad. In the United States, it is estimated that >4.4% of pregnant women abuse 1 or more substances during pregnancy. Social and environmental factors contribute significantly to increases in the prevalence and complexity of substance abuse disorders. Fear of reprisal prevents many women from accurately reporting substance use patterns and receiving appropriate medical and psychological care. This chapter details the epidemiology and risk factors associated with substance abuse during pregnancy and subsequent complications for the neonate.