Viral marketing refers to marketing techniques that use existing social networks to produce increases in brand awareness, through self-replicating viral processes, analogues to the spread of pathological and computer viruses. It can be word-of-mouth, delivered or enhanced by the network effects of the Internet.

Viral marketing is a marketing phenomenon that facilitates and encourages people to pass along a marketing message voluntarily. Viral promotions may take the form of funny video clips, interactive Flash games, adver-games, images, or even text messages.

It is claimed that a satisfied customer tells an average of three people about a product or service he/she likes, and eleven people about a product or service which he/she did not like. Viral marketing is based on this natural human behaviour.