Humans have altered terrestrial ecosystems for millennia 1, yet wilderness areas still remain as vital refugia where natural ecological and evolutionary processes operate with minimal human disturbance 2–4, underpinning key regional- and planetary-scale functions 5, 6. Despite the myriad values of wilderness areas—as critical strongholds for endangered biodiversity 7, for carbon storage and sequestration 8, for buffering and regulating local climates 9, and for supporting many of the world’s most politically and economically marginalized communities 10—they are almost entirely ignored in multilateral environmental agreements. This is because they are assumed to be relatively free from threatening processes and therefore are not a priority for conservation efforts 11, 12. Here we challenge this assertion using new comparable maps of global wilderness following methods established in the original “last of the wild” analysis 13 to examine the change in extent since the early 1990s. We demonstrate alarming losses comprising one-tenth (3.3 million km2) of global wilderness areas over the last two decades, particularly in the Amazon (30%) and central Africa (14%). We assess increases in the protection of wilderness over the same time frame and show that these efforts are failing to keep pace with the rate of wilderness loss, which is nearly double the rate of protection. Our findings underscore an immediate need for international policies to recognize the vital values of wilderness and the unprecedented threats they face and to underscore urgent large-scale, multifaceted actions needed to maintain them. •Globally important wilderness areas are ignored in conservation policy•We reveal that extensive losses of wilderness have occurred in the last two decades•Efforts aimed at protecting wilderness areas are failing to keep pace with its loss•International policy must recognize the actions needed to maintain wilderness areas Watson et al. discover that the Earth’s wilderness areas are disappearing at a rate that has significantly outpaced their protection over the past two decades. Despite their ecological, climatological, and cultural importance, wilderness areas are ignored in multilateral environmental agreements, highlighting the need for urgent global policy attention.