AbstractAutism spectrum disorder (ASD) is a heteroge-neous clinical condition whose prevalence has grown consid-erably during the last decade. Genetic factors are thought to underpin the disorder, but common genetic variants and epi-genetic mechanisms have been increasingly called into ques-tion for the majority of ASD cases. Growing prenatal expo-sure to new environmental toxicants has been shown to po-tentially affect brain development, leading to altered cogni-tive, social, attentive, behavioral, and motor performance. Both epidemiological evidence and mechanistic studies assessing oxidative stress, neuroinflammation, epigenetic al-terations, and impaired signal transduction, all observed fol-lowing neurotoxicant exposure, indeed lend biological plau-sibility toGene x Environment interactions, whereby environ-mental toxicants interacting additively or synergistically with genetic liability, can push prenatal neurodevelopmental pro-cesses over the threshold for postnatal ASD expression. Re-search on environmental contributions toASD and on specific Gene x Environment interaction models ultimately aims at defining targeted preventive strategies. KeywordsAir pollution.Autism.Autismspectrum disorder.Benzo(a)pyrene. Environment. Environmental factors. Halogenated aromatic hydrocarbons. Heavymetals. Mercury. Misoprostol.MMR. Organophosphates. PervasiveDevelopmental Disorders. PBDEs. PCBs. p-cresol. Pesticides. Polybrominated diphenyl ethers. Polychlorinated biphenyls.Thalidomide. Thimerosal. Vaccines.Valproate