Deep ocean observation is a science and technology challenge addressing the grand societal issues of climate change mitigation and adaptation, ecosystem exploration, sustainable management and conservation. The Deep Ocean Observing Strategy (DOOS) is a Global Ocean Observing System (GOOS) Project focused on the creation and implementation a collective statement of requirements and an initial strategy for sustained global deep-ocean observations for the next 10-50 years. The long-term requirements and strategy will be developed with consideration to all Essential Ocean Variables, regions, and technologies to ensure high impact, feasibility, and GOOS fit-for-purpose actions.