This paper provides a detailed analysis of how the European Emission Trading System (EU ETS) as the core climate policy instrument of the European Union has impacted innovation. Towards this end, we investigate the impact of the EU ETS on research, development and demonstration (RD&D), adoption, and organizational change. In doing so, we pay particular attention to the relative influences of context factors (policy mix, market factors and public acceptance) and firm characteristics (value chain position, technology portfolio, size and vision). Empirically, our qualitative analysis is based on multiple case studies with 19 power generators, technology providers and project developers in the German power sector which were conducted in 2008/09. We find that the innovation impact of the EU ETS has remained limited so far because of the scheme's initial lack of stringency and predictability and the relatively greater importance of context factors. Additionally, the impact varies significantly across technologies, firms, and innovation dimensions and is most pronounced for RD&D on carbon capture technologies and organizational changes. Our analysis suggests that the EU ETS on its own may not provide sufficient incentives for fundamental changes in corporate innovation activities at a level which ensures political long-term targets can be achieved.