Advertising is a form of communication that typically attempts to persuade potential customers to purchase or to consume more of a particular brand of product or service. Many advertisements are designed to generate increased consumption of those products and services through the creation and reinforcement of "brand image" and "brand loyalty".

For these purposes, advertisements sometimes embed their persuasive message with factual information. Every major medium is used to deliver these messages, including television, radio, cinema, magazines, newspapers, video games, the Internet and billboards. Advertising is often placed by an advertising agency on behalf of a company or other organization.

Organizations that frequently spend large sums of money on advertising that sells what is not, strictly speaking, a product or service include political parties, interest groups, religious organizations, and military recruiters. Non-profit organizations are not typical advertising clients, and may rely on free modes of persuasion, such as public service announcements.

Advertising spending has increased dramatically in recent years. In 2006, spending on advertising has been estimated at $155 billion in the United States and $385 billion worldwide, and the latter to exceed $500 billion by 2010.

While advertising can be seen as necessary for economic growth, it is not without social costs. Unsolicited Commercial Email and other forms of spam have become so prevalent as to have become a major nuisance to users of these services, as well as being a financial burden on internet service providers.

Advertising is increasingly invading public spaces, such as schools, which some critics argue is a form of child exploitation.

Egyptians used papyrus to make sales messages and wall posters. Commercial messages and political campaign displays have been found in the ruins of Pompei and ancient Arabia. Lost and found advertising on papyrus was common in Ancient Greece and Ancient Rome.

Wall or rock painting for commercial advertising is another manifestation of an ancient advertising form, which is present to this day in many parts of Asia, Africa, and South America. The tradition of wall painting can be traced back to Indian rock art paintings that date back to 4000 BCE.

As the towns and cities of the Middle Ages began to grow, and the general populace was unable to read, signs that today would say cobbler, miller, tailor or blacksmith would use an image associated with their trade such as a boot, a suit, a hat, a clock, a diamond, a horse shoe, a candle or even a bag of flour.

Fruits and vegetables were sold in the city square from the backs of carts and wagons and their proprietors used street callers or town criers to announce their whereabouts for the convenience of the customers.

As education became an apparent need and reading, as well printing developed, advertising expanded to include handbills. In the 17th century advertisements started to appear in weekly newspapers in England.

These early print advertisements were used mainly to promote books and newspapers, which became increasingly affordable with advances in the printing press; and medicines, which were increasingly sought after as disease ravaged Europe. However, false advertising and so-called "quack" advertisements became a problem, which ushered in the regulation of advertising content.