Viral marketing refers to the business practice of advertising or raising awareness through social circles, specifically social networks. A viral marketing campaign tries to either raise name recognition and brand popularity or to market a specific service or product, especially through online channels such as Facebook or MySpace. The goal of such a strategy is for word to pass quickly from person to person through contacts, groups, and friend lists, raising maximum awareness and buzz without using a large part of the marketing budget. Companies can do this through well-placed ads, creating their own social networking profiles, or spreading word through a number of pseudo profiles and messages. Businesses can also use multimedia aspects of social networking such as games to heighten pass-along numbers, or the percentage of people who pass the information along to their friends.

Viral marketing campaigns often cite Hotmail as being the first example of successful viral marketing.