Mercantilism is an economic theory which holds that the prosperity of a nation depends upon its supply of capital, and that the global volume of trade is "unchangeable." Capital, represented by bullion (gold or silver) held by the state, is best increased through a positive balance of trade with other nation (exports over imports). Mercantilism suggests that the ruling government should advance these goals by playing a protectionist role in the economy, by encouraging exports and discouraging imports, especially through the use of tariffs. The economic policy based upon these ideas is often called the mercantile system.

Mercantilism was the dominant school of economics throughout the early modern period (from the 16th to the 18th century, which roughly corresponded to the emergence of the nation-state). Domestically, this led to some of the first instances of significant government intervention and control over the economy, and it was during this period that much of the modern capitalist system was established. Internationally, mercantilism encouraged the many European wars of the period, and fueled European imperialism, as the European powers fought over "available markets". Belief in mercantilism began to fade in the late 18th century, as the arguments of Adam Smith, and the other classical economists won favor in the British Empire among such advocates as Richard Cobden and to a lesser degree in the rest of Europe with the notable exception of Germany where the Historical school of economics was favored throughout the 19th and early 20th century. Interestingly, the once former British colonies, the United States of America did not adhere to classical economics but to what is called the "American School" (a form of neo-mercantilism) in the policies of Hamilton, Clay, Lincoln and later Republican Party economic practices, that were mirrored in the policies of the Historicists in Germany by such economists as Friedrich List, until the emergence of the New Deal and the modern era. Today, mercantilism as a whole is rejected by many economists, though some elements are looked upon favorably by some economists including Ravi Batra, Pat Choate, Eammon Fingleton, and Michael Lind.

A number of scholars found important flaws with mercantilism long before Adam Smith developed an ideology that could fully replace it. Critics like Dudley North, John Locke, and David Hume undermined much of mercantilism, and it steadily lost favor during the eighteenth century. Mercantilists failed to understand the notions of comparative advantage (although this idea was only fully fleshed out in 1817 by David Ricardo) and the benefits of trade. For instance, Portugal was a far more efficient producer of wine than England, while in England it was relatively cheaper to produce cloth. Thus if Portugal specialized in wine and England in cloth, both states would end up better off if they traded. In modern economic theory, trade is not a zero-sum game of cutthroat competition, as both sides could benefit. By imposing mercantilist import restrictions and tariffs instead, both nations ended up poorer.

David Hume famously noted the impossibility of the mercantilists' goal of a constant positive balance of trade. As bullion flowed into one country, the supply would increase and the value of bullion in that state would steadily decline relative to other goods. Conversely, in the state exporting bullion, its value would slowly rise. Eventually it would no longer be cost-effective to export goods from the high-price country to the low-price country, and the balance of trade would reverse itself. Mercantilists fundamentally misunderstood this, long arguing that an increase in the money supply simply meant that everyone gets richer.

The importance placed on bullion was also a central target, even if many mercantilists had themselves begun to de-emphasize the importance of gold and silver. Adam Smith noted that bullion was just the same as any other commodity, and there was no reason to give it special treatment. Gold was nothing more than a yellow metal that was valuable only because there was not much of it.

The first school to completely reject mercantilism were the Physiocrats of France. Their theories also had several important problems, and the replacement of mercantilism did not come until Adam Smith published The Wealth of Nations in 1776. This book outlines the basics of what is today known as classical economics. Smith spends a considerable portion of the book rebutting the arguments of the mercantilists, though often these are simplified or exaggerated versions of mercantilist thought.

Scholars are also divided over the cause of mercantilism's end. Those who believe the theory was simply an error hold that its replacement was inevitable as soon as Smith's ideas that are more accurate were unveiled. Those who feel that mercantilism was rent-seeking hold that it ended only when major power shifts occurred. In Britain mercantilism faded as the Parliament gained the monarch's power to grant monopolies. While the wealthy capitalists who controlled the House of Commons benefited from these monopolies, Parliament found it difficult to implement them because of the high cost of group decision making.

Mercantilist regulations were steadily removed over the course of the eighteenth century in Britain, and during the 19th century the British government fully embraced free trade and Smith's laissez-faire economics. On the continent, the process was somewhat different. In France economic control remained in the hands of the royal family and mercantilism continued until the French Revolution. In Germany mercantilism remained an important ideology in the nineteenth and early twentieth centuries, when the historical school of economics was paramount.