In this contribution, the authors investigate the way partners involved in Complex Products and Systems (CoPS) development manage local standards. In particular, this paper analyses how this management impacts the relations between partners through their roles of leader and complementor within platforms. The results are based on a qualitative case study in the launch vehicle segment of the space sector, especially the development of the Ariane 5 and Vega European space launchers. First, the authors find that standards management reveals the firm's position in a platform as a leader or a complementor. Second, it is shown that standards can be a way for complementors to build new system skills by collaborating with platform leaders. Along with skill building, they allow a firm to challenge the dominant position of the platform leader. Third, the authors show that firms use local standards combined with alliance strategies to manage competitive tensions. Then, the paper discusses literature on standards in CoPS and on leader and complementor's positions within platforms.