In the last 30 years the role of purchasing has changed dramatically, from a clerical, administrative function into a strategic function that contributes to the competitive advantage. Companies need a variety of supplier relationships. In a seminal paper Kraljic (1983) introduced a portfolio approach for the development of appropriate purchasing and supplier strategies. In contrast with an ever increasing adoption of purchasing portfolio models, there are many unanswered questions concerning the theoretical foundations and the practical possibilities. This book reports on an extensive research to the foundations, the usefulness and the possibilities of the purchasing portfolio approach. The book provides a state of the art knowledge on purchasing portfolio models, informing and (preferably) inspiring a broad international, academic audience. In addition, the book introduces and describes a practical (research- based) outline for the application of the portfolio analysis, covering the main questions and issues that have to be addressed in practice. Therefore, the audience for this book are academic readers and business practitioners.