The Extinction of Worlds offers a new way of thinking about extinction. It argues that extinction events often involve experiential losses--the irrevocable disappearance of ways of experiencing. Picture the moment, roughly ten thousand years ago, when the very last woolly mammoth lay down, breathed its last, and lost consciousness. The world changed. A world containing mammoths became a world containing none. However, more than this, certain ways of experiencing the world disappeared. From that point forward, no animal would ever experience distinctively mammothish things in distinctively mammothish ways. More generally, when a conscious endling dies, certain ways of experiencing--those of its species--die with them. This, the author suggests, is one reason why such deaths are significant events. The arguments in support of this conclusion are developed over twelve chapters. Early chapters consider the experiential losses that can accompany personal extinction--that is, death. Later chapters address the decline and eventual disappearance of human and animal cultures, the extinction and de-extinction of biological species, and (looking far into the future) the death of the ultimate endling--the very last experiencing entity. The final chapter asks whether experiential loss is in any sense bad. Drawing on recent work in moral philosophy, the author argues that it can be extremely bad. Written in an accessible and engaging style, and drawing upon a wide range of philosophical, literary, and scientific sources, this book will appeal to anyone who wishes to explore the moral and metaphysical significance of extinction.