Trade is the transfer of goods or services in exchange for money. It seems to have developed along with civilization. The earliest known written records, from the 10th millennium BCE, are accounts of trade. Later, people established networks of trade over land and sea. Trade between Mesopotamia and the Indus Valley, and between Egypt and ancient China, was well established by the 1400s. By the 1600s, European countries had established colonies around the world, opening new trade routes and extending existing ones.

Many governments restrict trade to prevent companies from selling dangerous or illegal products, or from monopolizing the market for certain goods. Governments also set trading terms, such as tariffs and quotas, that traders must follow. Some countries restrict trade within their borders as well, to protect local industries from foreign competition.

International trade has become increasingly important as technology has improved and the economies of developing nations have grown. Trade can also be beneficial for both countries. For example, a country with plentiful natural resources for producing lumber can sell building supplies to a neighboring country that is short of those natural resources. This is an example of comparative advantage, a principle explained in 1776 by Adam Smith in An Inquiry into the Nature and Causes of the Wealth of Nations.

A trade publication is a collection of articles that address topics of interest to members of a particular profession, such as law enforcement or advertising or banking. They might include editorials, letters to the editor, photo essays, and advertisements. Unlike those in consumer magazines, ads in trade publications tend to focus on products or services that are specifically relevant to the profession being discussed. For example, police magazines often feature ads for bulletproof vests and nutrition magazines contain advertisements for equipment that helps readers track their weight loss.