The article investigates three mechanisms by which expectation dynamics affect innovation processes. Empirically, it focuses on hype-disappointment cycles in electronic commerce and interactive television, drawing on results from qualitative case studies and secondary analysis. First, two specific ways by which collective, i.e. widely shared, expectations motivate and guide innovation actors are presented. These mechanisms serve as an explanation for the fact that often an impressively large number of heterogeneous actors accept and contribute to high-rising expectations. With reference to a third mechanism, it is shown that results of technological projects are subject to interpretative flexibility and, as such, are interpreted in the light of the same expectations they are supposed to 'validate'. Sudden changes of the consideration of certain technologies as promising or not are then explained as a result of the interaction between collective expectations and expectations and outcomes at the project level.