NETs range from afforestation to bioenergy with carbon capture and storage. They are seen by many as instrumental in achieving the mitigation objectives of the Paris Agreement. However, uncertainty remains regarding the technical, economic, and political feasibility of the large-scale deployment of NETs. The focus in this chapter is on whether a state may lawfully presume, for instance in the course of determining its long-term low-greenhouse-gas-emission development pathway under Article 4(19) of the Paris Agreement, that a future large-scale deployment of NETs will be realized. Gareth Davies maintains that that makes perfect sense, not least because conventional mitigation methods are in the same boat (of uncertainty), and that in other respects as well conventional methods are on a continuum with NETs. By contrast, Duncan McLaren and Wil Burns argue that any heavy reliance now on a presumed large-scale availability of NETs in the future would be irresponsible, unethical, and unlawful.