Non-linearity and changes in the direction of technological trajectories, are related to changes in cognitive rules and expectations that guide technical search and development activities. To explain such changes, the article uses the literature on niche development, which highlights interactions between learning processes, network building and expectations. A long-term case study on Dutch biogas development illustrates how these interactions explain non-linearity, but the case study also shows the importance of external regime dynamics. It is concluded that non-linearity and changes in niche expectations are related to both internal learning processes and external developments. © 2006 Taylor & Francis.