This briefing paper discusses the potential risks associated with plans to mine the deep seabed of minerals, and how financial institutions should respond to the deep-sea mining sector. The briefing paper aims to provide an initial framework for this broad variety of institutions to consider how sustainability impacts and risks specific to harmful and non-renewable marine extractives manifest within their own portfolios, as well as the potential business risks arising from financing such activities. Given the breadth of this subject matter and the relevance of sustainability considerations to a broad array of stakeholders, this information may also be valuable to the public sector, intergovernmental organizations, academia, civil society, commerce and industry.