This book pay attention on relationship marketing because it has recognized the importance of building long-term relationships in increasing firms' profitability and guaranteeing their future viability. Owing to the damaging effects, that customer switching behavior could have on the development of successful relationships, understanding customers' switching decisions can represent a key step in the process of establishing, developing and maintaining successful relational exchanges. Aim of this book is to introduce the heterogeneity of customers in their relationship characteristics (depth, length and breadth) into the analysis of customers' retention to switch service providers. By considering the moderating role of relationship characteristics with the customers' retention, the relationship characteristics do moderate the relationship between service quality and customer retention. If service providers want to keep their customer retain, towards their services and products, they should compete on service quality.