This chapter examines the issues around setting biomass sustainability as an essential element to a future bioeconomy. Use of biomass for bio-based production in ambitious bioeconomy plans is fraught with the risk of unsustainable, over-exploitation of natural resources. Developing only modest bioeconomy strategies is one option, but may not achieve the longer-term goals of highly ambitious reductions of greenhouse gas (GHG) emissions. Another option is to create ambitious bioeconomy plans that make biomass production and use more efficient. However, studies also point out that more land is needed to produce biomass. So a dual strategy can be envisioned – land intensification and extensification. Each brings its own problems; the most frequently discussed relate to sustainability, and the inevitable competition for land between food and industrial use. There is no international agreement yet on how to measure biomass sustainability. As a result, estimates of biomass potential (how much can be grown sustainably) vary greatly. New institutions may be necessary to harmonise sustainability assessments.