Marine science is now moving quickly to reveal the biophysical, geochemical, and ecological properties of the deep sea. As this understanding grows, deep-sea resources will begin to be exploited more extensively, embodying the hopes of many for a Blue Economy. Institutions to govern this exploitation are only just finding their strides or even just emerging, but there are many cases already of resource overuse and degradation, including overfishing and the impacts beginning to be wrought by a changing climate. Progress towards the sustainable development of the deep sea requires useful indicators that point to changes in human well-being as the deep sea is exploited, such as measures of inclusive wealth. Accounting prices for the natural capital of the deep sea would be useful indicators, and several examples are explored to illustrate current understanding and research gaps. A future economic research agenda would involve refining estimates of accounting prices for the most important types of deep-sea natural capital, locating these within linked classifications of ecosystem services and natural capital, and the design and implementation of a system of economic and environmental accounts for the deep sea comprising the high seas, which lies beyond the purview of individual states.