Reproduction and developmental damage has irreversible consequences compared to other body functions and may have adverse effects throughout life. In some circumstances, the damage passes from generation to generation. Many environmental agents contribute to developmental toxicities such as toxic metals, insecticides or pesticides, commercial or industrial pollutants, and air pollutants. Increased urbanization and industrialization have led to the accumulation of toxic metals in the environment. Widespread use of heavy metals in different fields such as agriculture, domestic, medical, industrial, and technological applications have resulted in increased exposure of heavy metals to the human population. Environmental exposure to heavy metals is extensively linked to toxic effects on mammalian embryos. Metals such as lead, cadmium, mercury and arsenic are known developmental toxicants that intensely affect fetal and embryonic development and cause certain malformations in developing embryo even at low concentrations. Other metals such as uranium, cobalt, lithium, Aluminium, manganese, and copper are also reported to induce developmental consequences, including neurobehavioral abnormalities, neural tube defects, fetal growth retardation, skeletal deformation, preterm or delayed birth, and still birth or postnatal death. Heavy metal developmental toxicity depends on different factors, including dose, duration, and route of exposure. Hence, heavy metals are known to be toxic to fetal and embryonic tissues and can produce serious teratogenicity in mammals; however, not much attention has been given to this topic. This chapter, therefore, summarizes the developmental toxicity of heavy metals on the mammalian system and their teratogenic mechanism in growing embryos.