The article presents a global assessment of progress toward protecting 50% of the terrestrial biosphere to address the species-extinction crisis and conserve a global ecological heritage for future generations. Using a map of Earth's 846 terrestrial ecoregions, the authors show that 98 ecoregions (12%) exceed Half Protected; 313 ecoregions (37%) fall short of Half Protected but have sufficient unaltered habitat remaining to reach the target; and 207 ecoregions (24%) are in peril, where an average of only 4% of natural habitat remains. The authors propose a Global Deal for Nature—a companion to the Paris Climate Deal—to promote increased habitat protection and restoration, national- and ecoregion-scale conservation strategies, and the empowerment of indigenous peoples to protect their sovereign lands. The goal of such an accord would be to protect half the terrestrial realm by 2050 to halt the extinction crisis while sustaining human livelihoods. The authors argue that the Aichi target of protecting 17% of terrestrial land and inland water areas by 2020 is insufficient, as it does not meet the science-based level of protection required to achieve comprehensive biodiversity conservation. They propose a 50% protection target, which is supported by scientific analyses and advocacy papers under the name "Nature Needs Half." The authors evaluate progress toward this goal within the framework of ecoregions, protected areas, and habitats. They answer two basic questions: (1) Is the aspirational goal of protecting half of nature in the terrestrial realm possible? (2) Which half should be protected, and how much of it has already been conserved? The authors revised the 2001 map of terrestrial ecoregions and determined the extent of both protected areas and remaining natural habitat within each ecoregion. They used the World Database of Protected Areas to designate the protected area network and tree-cover maps in forested ecoregions to assess habitat. The analysis shows that 98 ecoregions (12%) have already achieved Half Protected, while 313 ecoregions (37%) have enough remaining natural habitat to reach Half Protected if additional protected areas or other types of conservation areas are added to the system. The remaining 207 ecoregions (24%) are in peril, where the sum of the amount of natural habitat remaining and the amount of the total ecoregion that is protected is less than or equal to 20%. The authors also highlight the importance of protecting key biodiversity areas and the need for effective implementation of conservation strategies. They provide examples of successful conservation efforts in Namibia, Nepal, and Bhutan, where local communities have played a key role in protecting biodiversity. The authors argue that the 50% protection target is achievable in many of the Earth's more intact eThe article presents a global assessment of progress toward protecting 50% of the terrestrial biosphere to address the species-extinction crisis and conserve a global ecological heritage for future generations. Using a map of Earth's 846 terrestrial ecoregions, the authors show that 98 ecoregions (12%) exceed Half Protected; 313 ecoregions (37%) fall short of Half Protected but have sufficient unaltered habitat remaining to reach the target; and 207 ecoregions (24%) are in peril, where an average of only 4% of natural habitat remains. The authors propose a Global Deal for Nature—a companion to the Paris Climate Deal—to promote increased habitat protection and restoration, national- and ecoregion-scale conservation strategies, and the empowerment of indigenous peoples to protect their sovereign lands. The goal of such an accord would be to protect half the terrestrial realm by 2050 to halt the extinction crisis while sustaining human livelihoods. The authors argue that the Aichi target of protecting 17% of terrestrial land and inland water areas by 2020 is insufficient, as it does not meet the science-based level of protection required to achieve comprehensive biodiversity conservation. They propose a 50% protection target, which is supported by scientific analyses and advocacy papers under the name "Nature Needs Half." The authors evaluate progress toward this goal within the framework of ecoregions, protected areas, and habitats. They answer two basic questions: (1) Is the aspirational goal of protecting half of nature in the terrestrial realm possible? (2) Which half should be protected, and how much of it has already been conserved? The authors revised the 2001 map of terrestrial ecoregions and determined the extent of both protected areas and remaining natural habitat within each ecoregion. They used the World Database of Protected Areas to designate the protected area network and tree-cover maps in forested ecoregions to assess habitat. The analysis shows that 98 ecoregions (12%) have already achieved Half Protected, while 313 ecoregions (37%) have enough remaining natural habitat to reach Half Protected if additional protected areas or other types of conservation areas are added to the system. The remaining 207 ecoregions (24%) are in peril, where the sum of the amount of natural habitat remaining and the amount of the total ecoregion that is protected is less than or equal to 20%. The authors also highlight the importance of protecting key biodiversity areas and the need for effective implementation of conservation strategies. They provide examples of successful conservation efforts in Namibia, Nepal, and Bhutan, where local communities have played a key role in protecting biodiversity. The authors argue that the 50% protection target is achievable in many of the Earth's more intact e