Technical Abstract: Extreme summer time conditions can have a devastating impact on livestock, especially those animals who are typically housed outdoors without shelter, such as feedlot cattle. The effect of heat stress on feedlot cattle can vary from little to no effect in a brief exposure, to causing reductions in feed intake, growth, and feed efficiency in a moderate event, to death of vulnerable animals during an extreme event. Heat stress can be broken down into three sub-components: environmental conditions, susceptibility of the individual animal, and the management options employed. This chapter describes the economic impact of heat stress, factors affecting an individual animal’s susceptibility to heat stress, and the management options that can be used to decrease the impact. In addition, the chapter will start to layout the means to combine these three factors into a management strategy.