This paper describes some of the key challenges to be met in the development of marine renewable energy technology, from its present prototype form to being a widely deployed contributor to future energy supply. Since 2000, a number of large-scale wave and tidal current prototypes have been demonstrated around the world, but marine renewable energy technology is still 10–15 years behind that of wind energy. UK-based developers are leading the way, with Pelamis from Pelamis Wave Power demonstrated in the open sea, generating electricity into the UK network and securing orders from Portugal. However, having started later, the developing technology can make use of more advanced science and engineering, and it is therefore reasonable to expect rapid progress. Although progress is underway through deployment and testing, there are still key scientific challenges to be addressed in areas including resource assessment and predictability, engineering design and manufacturability, installation, operation and maintenance, survivability, reliability and cost reduction. The research priorities required to meet these challenges are suggested in this paper and have been drawn from current roadmaps and vision documents, including more recent consultations within the community by the UK Energy Research Centre Marine Research Network. Many scientific advances are required to meet these challenges, and their likelihood is explored based on current and future capabilities.