This article presents an economic perspective of the institution of slavery in the context of world and American history. Slavery has existed on all continents and in many societies. Its existence has long been controversial and, in the case of the United States, ended only as the result of a long and destructive war. Slavery as an institution was nearly universal throughout world history. People in the ancient Near East--as well as in Asia, Europe, Africa, and America before the arrival of the Europeans--all enslaved people, in varying degrees and circumstances. Slavery was an institution that dominated the economy of the American South from the mid-1600s to 1865. Was slavery profitable? The answer is "yes," according to most economic historians. The system of slavery operated, in many ways, like a modern market. It involved buyers, sellers, prices, trade, production, distribution, and investments. At its root, it depended on coerced, involuntary exchanges. Enslaved people never gave their consent to be involved in any transaction with slave holders. The institution of slavery was intellectually unchallenged for centuries. Yet, at its economic height as an institution, moral doubts were expressed by intellectuals sympathetic to political and economic liberty. These ideas were eventually accepted and laws changed as a result. While historians and economists may debate this for years to come, perhaps it was the inherent contradiction between economic freedom and slavery that made the difference.