An organization's ability to create, retrieve, and use knowledge to innovate is a critical strategic asset. Until recently, most textbooks on business and product development argued that managers should keep their new ideas to themselves and protect knowledge from getting into competitors' hands. Seeking, developing, and protecting knowledge is a costly endeavour. Moreover, apart from being expensive, the process of turning new knowledge into useful and well-protected innovations often slows the speed of development and increases costs. In this chapter, alternative strategies for innovation, in which sharing and cooperation play a critical part, are discussed. In particular, we address the involvement of users in opening up the innovation process which, in turn, offers participating actors some useful strategies for product development. Four archetypal strategies are identified and classified according to type of user involvement and the organizational level at which cooperation with external sources of knowledge takes place.