When discussing the extinction of humanity, there does not seem to be any clear agreement about what ‘humanity’ really means. One aim of this paper is to show that it is a more slippery concept than it might at first seem. A second aim is to show the relationship between what constitutes or defines humanity and what gives it value. Often, whether and how we ought to prevent human extinction depends on what we take humanity to mean, which in turn (...) depends on what we value about humans. Finally, I will offer a definition of humanity that I argue offers a plausible account of when we might say humanity has gone extinct, and reflects what we value about humans, and relatedly, what many actually care about in terms of why we should be preserved. (shrink)