Environmental endocrine disruptors are man-made chemicals that can disrupt the synthesis, circulating levels, and peripheral action of hormones. Thyroid hormones are required for normal brain and body development and for the proper physiological regulation in both children and adults. The environmental chemicals may act as disruptors at all levels of thyroid homeostasis. The EDCs interferes both the production and distribution of THs by lowering the Serum T4 and T3 levels, increased activity of metabolizing enzymes in the liver, Decreased activity of iodothyronine deiodinases etc. Endocrine-disrupting chemical are categorized into two groups: one having structural similarity with TH and other as competitors to iodine uptake. Chemicals like polychlorinated biphenyls and Tetrabromobisphenol have structural similarity with TH and perchloate and thiocyanate act as competitors to iodine uptake. This chapter also includes studies on thyroid-disrupting chemicals in India.