Viral marketing involves consumers passing along a company’s marketing message to their friends, family, and colleagues. This chapter reviews viral marketing campaigns and argues that the emotion of surprise often is at work and that this mechanism resembles that of word-of-mouth marketing. Examining the literature on the emotion of surprise, the chapter next explains how a surprise is created and shared. Overall, the chapter shows how surprise can be a useful tool in a viral marketing campaign. Lastly, conclusions of interest to managers are drawn.