The Plan of Renewable Energies 2005-2010, in Spain raised an ambitious objective: at least, 12% of the total energy consumption must come from renewable sources in 2010. Nevertheless, no form of marine energy is among the research and development areas identified by the above mentioned Plan. One of them, wave energy technology, is still in an embryonic phase of development, but it has the potential of helping to reach the objectives of renewable energy production proposed by the Plan. For this purpose, as well as solving the technical difficulties of the development of the wave energy devices, we must clear the uncertainties and address the likely environmental effects that this kind of technologies could produce on the marine environment during installation, operation and decommissioning. In this context, the Ministry of Science and Innovation of the Spanish Government launched in 2005, the Strategic Outstanding Project on Marine Energy, led by Tecnalia (www.tecnalia.es). The main objective of this project is the technological development of marine energy converters; the project joins together the main Spanish developers of these devices and the supporting industry and technology agents, the latter being led by Tecnalia. Within this project, the 5th work package (WP), devoted to the study of the environmental impact of wave energy converters on the marine environment, is led by AZTITecnalia (www.azti.es). The main objective of this WP is to provide the basic information, specific data, and the analysis, study and evaluation methodologies needed for the adequate environmental impact assessment of the marine wave energy technologies. Most environmental effects of these technologies may be limited to the operational life of any device deployment. Effects on physical environment can be restricted to the placement of hard structures and cables, visual impacts, noise and modification of the local hydrodynamic environment. Effects on the biota cannot be defined with certainty. Monitoring and mitigation by adaptive management will address specific issues as they arise. This work provides an early-stage review of likely environmental effects of wave energy to inform project developers, territorial authorities and interested parties. It aims to introduce a first step to developing a risk management framework, which future project developers and territorial authorities can use to predict, prevent and deal with the environmental impacts of the deployment of wave energy converters in Spain.