This paper examines the role that communities of practice (CoPs) of farmers play in the innovation process. The Agricultural Innovation Systems approach focuses mainly on interactions and learning between farmers and other actors but less on collective processes occurring between farmers. In CoPs farmers not only collectively construct knowledge, but also produce and reproduce discourses and norms providing framework for individual actions, that both can hamper or support innovation. We combined different qualitative methods to explore the role of CoPs of dairy farmers in three on-going innovation projects in an irrigated perimeter in North-West Tunisia. We found farmers belonging to CoPs more empowered for innovation that those working individually with expert support. However, this was only true in the CoPs where access to external sources of knowledge was assured. Addressing farmers as collectively constructing knowledge and opening space for negotiation of meanings were conditions determining the success of one of the innovation projects. CoP's ability to collectively produce discourse should be used and farmers should be supported in developing innovation narratives. This implies sharing power with farmers over the innovation process.