With the advent of the web 2.0 trend, there have appeared a great variety of ser-vices that are offered as free. Although the appearance of free services is not new, we consider that the popularity of these services in the Web 2.0 world is a relevant fact that has to be analyzed from an economic point of view. In this chapter we will give an overview of some of the business models that are present behind those services, like freemium, advertising, work exchange and mass collaboration. We will also present a case study, called EuroAlert, which contains a combination of the above models.