Canada’s vast, highly energetic coastal waters make ocean renewable energy, particularly wave energy conversion (WEC) and tidal in-stream energy conversion (TISEC), technologies an attractive option to help meet the country’s future energy needs. As with other marine developments, activities associated with construction, operation and decommissioning of ocean renewable energy technologies have the potential to impact marine ecosystems and organisms, both at local (near-field) and regional (far-field) scales. To support the development of policy and regulations to govern the Canadian TISEC and WEC industry, a scientific overview of potential environmental impacts associated with the deployment of these marine energy devices was conducted. Identified issues of concern included changes in physical processes (wave, current and sediment transport regimes), habitat loss and alteration, contaminants, electromagnetic fields, noise and vibrations and the physical interaction between energy conversion devices and living organisms. Consideration is also given to the application of potential mitigation measures and the identification of knowledge gaps and research needed to address future regulatory compliance requirements in Canada. Due to the novelty of WEC and TISEC technologies, there is still a great deal of uncertainty surrounding their potential environmental implications. The review of current scientific publications and technical reports indicate that few TISEC or WEC devices have undergone comprehensive environmental impact assessments using predictive numerical models and/or field trials. Practical experience with these technologies in Canadian waters is almost non-existent. The limited number of scientific publications or systematic research data available creates a major hurdle for evaluating environmental risks associated with emerging ocean renewable energy technologies. This document identifies the major issues of concern that require further scientific study to support the development of policy, regulations and operational guidelines to ensure the protection of our marine environment and the organisms that live in it.