Autism spectrum disorders (ASD) are highly heterogeneous developmental conditions characterized by deficits in social interaction, verbal and nonverbal communication, and repetitive patterns of behavior and movements. This article reviews the impact of genetic and environmental risk factors on ASD and their adverse physiological mechanisms. Although the involvement of genetic abnormalities in autism spectrum disorders is well-accepted, recent studies point to an equal contribution by environmental factors. So, here we focus on several environmental factors associated with the development of ASD like pesticides, phthalates, polychlorinated biphenyls, solvents, air pollutants, fragrances, glyphosate, heavy metals especially aluminum used in vaccines as adjuvant, volatile organic compounds and organic endocrine-disrupting compounds such as flame retardants, non-stick chemicals, phthalates, and bisphenol A. Toxicants implicated in ASD included pesticides, phthalates, polychlorinated biphenyls (PCBs) , though strongest evidence found for air pollutants and pesticides. Some gene variants in ASD confer altered vulnerability to environmental stressors and exposures.