Environmental temperature affects the quality of both human and animal life. Exposure to extremes in environmental temperatures often elicits a stress response which can compromise the productivity and well-being of domestic animals. For swine, both cold and hot environmental temperatures can be detrimental to overall productivity and well-being. The impact of thermal stress on survival, performance, and productivity is evident in all stages of swine production. Thermal stress is associated with reduced survival of the baby pig, poor reproductive performance in adult pigs, and poor growth and carcass quality in market pigs. Thermal stress invokes numerous changes in the pig’s metabolism, behavior, and endocrine system. At birth, baby pigs have a limited ability to cope with environmental stressors (cold, disease, limited nutrition) that predispose it to relatively high rates of neonatal morbidity and mortality. In contrast to older pigs, the early neonatal piglet does not increase its intake in response to cold temperature. Intake actually decreases during cold exposure, increasing the likelihood of starvation. Unlike the young pig, in which exposure to cold stress poses major health risks, in older pigs, exposure to heat stress hinders performance and productivity. At high ambient temperatures, sufficient feed intake by the sow is likely a greater concern for piglet survival and performance. Exposure to ambient temperatures greater than 25 degrees C decreases intake in lactating sows, resulting in reduced milk production and associated piglet growth. In boars, heat stress has been shown to alter sperm cell count and quality, thus decreasing reproductive efficiency and capabilities. Finally, in market pigs, heat stress has been reported to reduce growth rate and alter carcass composition. Therefore, heat stress not only reduces overall productivity in market pigs, but also reduces the value of the final product. Given the associated economic losses due to thermal stress in pigs, continued research on the influence of environmental temperature on pig productivity and well-being are undoubtedly needed and warranted.