Marine energy technologies can contribute to meeting sustainability challenges, but they are still immature and dependent on public support. This paper employs the Technological Innovation Systems (US) framework to analyze the development and diffusion of Swedish marine energy up until 2014. While there were promising device developers, relevant industrial capabilities, and world-class research, the system suffered from weaknesses in several important innovation processes. Finally, the analysis identifies the lack of informed political direction as a critical blocking factor and highlights its connection to domestic market potential.