The purpose of this dissertation is to study the operationalization of manufacturing flexibility, focusing on aspects of relationships in the supply chain and their impact on manufacturing flexibility. The research involves four manufacturing companies for studying the influence of four aspects of buyer-supplier relationship - trust/commitment, information sharing, supplier development and joint product development - on three external dimensions of manufacturing flexibility - mix, new products and volume. The study also observes the generalized effects of these relationships on manufacturing performance and on the levels of manufacturing flexibility shown by the companies studied. The buyer-supplier relationships are deeply analyzed and their general characteristics and effects on the operationalization of manufacturing flexibility are presented. In addition, the analysis of scope and achievability factors indicated the presence of little explored flexible resources in the companies studied. Finding ways for operationalizing flexibility must be seen as a priority question to obtain competitive advantage in manufacturing systems. This work shows how the relationships between the buyer and supplier can influence several external dimensions of manufacturing flexibility and, consequently, manufacturing performance.