Throughout most of Earth’s history, species disappeared at an average rate of 1 to 5 per year. Fossil evidence shows that five mass extinction catastrophes have occurred. Scientists estimate that we are witnessing the sixth mass extinction; species are currently disappearing at 1,000 to 10,000 times the normal background rate. This Great Problems Seminar will examine scientific debates about past and present causes of extinction, the factors that contribute to vulnerability or resiliency of endangered species, and the consequences (to the planet, to regional ecosystems, and to human societies and economies) of species loss. Where are extinctions currently having the greatest impact? How might conservation efforts prevent extinctions? What can we expect from efforts to revive extinct species? Student project groups will focus on specific extinction-related problems, and develop and present sustainable solution approaches based on their investigations. 2017-2018 is the first year for this theme.