Viral marketing is on everyone's lips. Nowadays, it is not uncommon to receive a viral message, such as a funny video, forwarded or recommended over the internet by family members, friends, acquaintances, or study/work colleagues. Marketers are increasingly asking themselves whom to send which viral messages to on the internet. This book first outlines the fundamentals of viral marketing. Based on the insights gained, it aims to apply Rogers' diffusion theory model to the spread of viral messages online. Three criteria (characteristics of adopters, content quality of the viral message, and interpersonal networks) are analyzed in detail, and seven hypotheses are formulated to provide insights into the willingness to forward viral messages. A quantitative survey among 18 to 29-year-olds is used as the empirical analysis method. The book is aimed at executives in marketing, e-commerce, and new media, as well as researchers and students in these fields.