Despite many years and dollars spent on public education to expose the dangers of tobacco smoking and second-hand smoke, smoking persists. Not only that, we now worry about the potential dangers of third-hand smoke (the residue left on surfaces where smoking has occurred), devices offering new ways to smoke (vaping) and the legalization and resultant expansion of the many ways to use cannabis. New research is expanding the vast literature on, and revealing new adverse effects of exposure to tobacco smoke during pregnancy, while nascent research on vaping and cannabis use in pregnancy is just beginning to emerge. Vaping and cannabis are perceived by many to be safe for use in pregnancy, but public health and medical organizations have issued strong warnings against both. This special issue presents focused reviews that lay out what we know about some of the effects of these exposures during pregnancy and the vulnerable adolescent years (Figure 1), and the diverse approaches used to elucidate these effects.

We have known for decades that tobacco smoke is a human developmental toxicant and teratogen, and new knowledge continues to emerge about the adverse effects of tobacco smoke on the outcome of pregnancy. We now understand that, in addition to maternal smoking, exposure of pregnant women to second-hand smoke is also developmentally toxic, as is periconceptual paternal smoking. Seven U.S. Surgeon General’s Reports since 1964 have addressed the effects of tobacco smoke on pregnancy, the latest of which finds a causal link between maternal smoking and orofacial clefts in offspring and suggestive causal links to clubfoot, gastroschisis and atrial septal defects (USDHHS, 2014). The range of known adverse effects and targets of tobacco smoke exposure during development continues to expand. Surprising links between maternal tobacco smoke exposure during pregnancy and elevated risk of obesity in adolescent offspring (Rogers, in this issue) probably represent the strongest evidence in humans that developmental exposure to environmental chemicals can raise the risk of obesity later in life, and such chemicals have been termed “obesogens” (Janesick & Blumberg, 2016).