Book excerpt: Social networks and word-of-mouth marketing are increasingly important, yet few current practices are based on a deep understanding of how the structure of networks can affect customer behavior and marketing outcomes. This chapter offers some critical observations on current word-of-mouth marketing practices and identifies four key questions that managers need to ask themselves before engaging in campaigns designed to leverage customer networks: Can we be confident that interpersonal influence or social contagion is really important? Why exactly would social contagion occur? Should we target key influentials? Can we identify and target those influentials? The answers to these questions cannot be taken for granted.