This chapter focuses on the mechanisms by which environmental exposures can induce endocrine disruption. It highlights the mechanisms that play important roles in developmental programming. Endocrine-disrupting chemicals, which mimic the activity of endogenous hormones and activate receptors are termed agonists, whereas those that inhibit receptor activity are termed antagonists. During the perinatal period programming of the endocrine axis occurs, making this a vulnerable period of exposure to endogenous and exogenous stimuli. Among the endocrine-disrupting chemicals (EDCs), xenoestrogens have garnered a significant amount of attention due to the well-known effects of the xenoestrogen diethylstilbestrol (DES) in humans, and the identification of many other estrogenic anthropogenic chemicals. Metabolism plays a key role in maintaining hormone homeostasis. Endocrine-disrupting chemicals can disturb normal hormone homeostasis, which can have both direct and indirect effects on the reproductive function of both wildlife and human populations.