This article proposes a review of the literature, consisting of a presentation of research from three disciplines at the source of the contemporary approach to viral marketing: the sociology of interpersonal relations; word-of-mouth marketing which integrates and adapts the main results of the preceding approach to marketing science; and the mathematical and statistical analysis of networks. In so far as viral marketing is commonly defined as an extension of word-of-mouth marketing to digital technologies and Internet, the main aim of this article is to present in more detail than usual the studies that today are sometimes over-simplified, overlooked or poorly retranslated.