The MIDAS project addresses fundamental environmental issues relating to the exploitation of deep-sea mineral and energy resources; specifically polymetallic sulphides, manganese nodules, cobalt-rich ferromanganese crusts, methane hydrates and the potential mining of rare earth elements. These new industries will have significant impacts on deep-sea ecosystems, in some cases extending over hundreds of thousands of square kilometres. Scientific knowledge is needed urgently to develop guidelines for industry ensuring wealth creation and Best Environmental Practice. MIDAS will assess the nature and scales of the potential impacts including 1) physical destruction of the seabed by mining, the creation of mine tailings and the potential for catastrophic slope failures from methane hydrate exploitation, 2) the potential effects of particle-laden plumes in the water column, and 3) the possible toxic chemicals that might be released by the mining process. Knowledge of the impacts will be used to address the key biological unknowns, such as connectivity between populations, impacts of the loss of biological diversity on ecosystem functioning, and how quickly the ecosystems will recover. The information derived will be used to guide recommendations for best practice, iterating with MIDAS industry partners and the wider stakeholder community to ensure that solutions are practical and cost-effective. We will engage with European and international regulatory organisations to take these recommendations forward into legislation in a timely fashion. A major element of MIDAS will be to develop methods and technologies for 1) preparing baseline assessments of biodiversity, and 2) monitoring activities remotely in the deep sea during and after exploitation (including ecosystem recovery). The MIDAS partnership represents a unique combination of scientists, industry, social scientists, legal experts, NGOs and SMEs.