This SpringerBrief offers a state of the art analysis of electronic word-of-mouth (eWOM) communications and its role in marketing. The book begins with an overview of traditional word-of-mouth (WOM) and its evolution to eWOM. It discusses the differences between traditional and online WOM. The book examines why people engage in eWOM communications, but also how consumers evaluate its persuasiveness. It also looks at the effects of eWOM. The book identifies current gaps in the eWOM research, but also highlights future directions for this growing field.