Viral marketing and viral advertising refer to marketing techniques that use social media and social networks to produce increases in brand awareness and product sales through digital viral processes, analogous 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 video clips, corporate blogging, interactive Flash games, advergames, ebooks, brandable software, images, or even text messages. The basic form of viral marketing is not infinitely sustainable.