This chapter focuses on adverse events occurring between fertilization and birth. It also talks about pollutants whose sources are mainly in the outdoor air. For many environmental contaminants, exposure levels fluctuate over time, and assessing exposure only once during the pregnancy generally yields a poor picture of the biologically relevant exposure. Tobacco smoke is a mixture of thousands of compounds present in gaseous form or as particulate matter. As for air pollutants, exposure to drinking-water contaminants is widespread and a low increase in risk may contribute to a sizeable proportion of cases of adverse pregnancy outcomes. Organic solvents are ubiquitous in non-occupational settings and they also constitute one of the most frequent classes of chemicals in both female and male working environments. Ionizing radiations are heterogeneous in terms of energy, physical nature, and ability to be absorbed by human tissues.