Co-opetition is a new field of business and of thinking. It occurs when companies collaborate joining their efforts for creating new value, while maintaining their rivalries, aspiring to outperform the other firms in the network. This new perspective advocates companies to create new business strategies and develop new capabilities that deal with the paradoxical behaviors of collaboration and competition simultaneously. The purpose of this dissertation is to investigate the motivation of competing companies to pursue a co-opetitive strategy. A theoretical framework, based on an exploratory case study of the International Postal System (IPS), standard application software to manage the international mail in the postal industry, is developed examining the different co-opetitive strategies for firms in a Standards Setting Organization. It determines the factors, at an industry and firm levels, which affect the firm's choice of a certain level of co-opetition and discusses the possible outcomes for firms engaged in such a behavior. Moreover, the study proposes a model examining the impact of co-opetition on a firm's performance, and identifying three sources enabling the firm to manage co-opetition, i.e., network resources, absorptive capacity and relational governance. The model, by defining the notion of co-opetitive performance based on value creation and appropriation, advances current research on co-opetition. The model also draws on multiple perspectives, such as the Resource-based and the Relational Views, to delineate mechanisms through which each of the examined sources affects common and private benefits, and in turn, the firm's performance. Data was collected by conducting a survey among postal operators, users of the IPS standards. To test the hypothesis, several statistical techniques were used, including multiple linear regressions and structural equation modeling (PLS). The findings are original in that they show that firms pursuing a co-opetitive strategy achieve superior performance as compared to the ones pursuing collaborative or competitive behaviors in isolation. This study also concludes that the collaborative and competitive performances among the firms in a co-opetitive network vary and highlights the need for a firm to develop the appropriate set of resources balancing between these two paradoxical performances. This dissertation makes a unique contribution to the literature of strategy in the area of co-opetition. It advances our understanding about the strategies and mechanisms that firms develop when co-opeting with rivals. It also provides empirical evidence that firms co-opeting with rivals achieve superior performance to firms collaborating or competing separately. The findings have also important practical implications for managers, by providing them with tools to devise the appropriate co-opetitive strategy of the firm and to develop mechanisms to outperform their rivals in the network.