Content becomes viral when, thanks to the use of digital media, it is spread fast, far and wide. Just like a virus, the more content is exposed to a multitude of people, the greater the chance that it will expand and “take root”, virtually, without limits. Sharing is what makes content go viral; but this is not a new concept, it is simply the evolution of word-of-mouth. What is revolutionary, compared to the classic marketing methods used in the past, is the speed with which content can spread, thanks to the digital world. By bringing together knowledge from various disciplines, such as mathematics, psychology and economics, it is possible to explain not only why certain content goes viral, but also to predict strategies and techniques that allow images, information and videos to reach millions of people in just a few seconds. At the root of this dynamic, there is only one factor we need to consider: motivation. Viral marketing studies and analyses what motivates people to share content.