Viral marketing, viral advertising, or marketing buzz are buzzwords referring to marketing techniques that use pre-existing social networks to produce increases in brand awareness or to achieve other marketing objectives (such as product sales) through self-replicating viral processes, analogous to the spread of viruses or computer viruses (cf. memes and memetics). It can be delivered by word of mouth or enhanced by the network effects of the Internet. Viral marketing may take the form of video clips, interactive Flash games, advergames, ebooks, brandable software, images, or text messages.

The ultimate goal of marketers interested in creating successful viral marketing programs is to create viral messages that appeal to individuals with high social networking potential (SNP) and that have a high probability of being presented and spread by these individuals and their competitors in their communications with others in a short period of time.

The term "viral marketing" has also been used pejoratively to refer to stealth marketing campaigns—the unscrupulous use of astroturfing online combined with undermarket advertising^{[clarification needed]} in shopping centers to create the impression of spontaneous word of mouth enthusiasm.