This research presents and analyzes an empirically grounded account of a new trend, open innovation, in the IT industry. The case depicts another new trend, innovation through customization of standard software as a business model, and we investigate the open innovation activities of an interorganiza tional network which consists of a small customizing company, a large global software producer, and other companies involved in the innovation process. We contribute to the development of a theory of open IT innovation with a theoretical framework that integrates formally separate aspects of open innovation and interorganizational networks. We extend the literature on open innovation by broadening the view from one focal firm to the relations in a network of companies that mutually contribute to innovation which occur in the different companies. Our research underlines the importance of balanced formal and informal relations, and coopetive and opportunistic behavior for the open innovation process.