‘Longtermism’ is the idea that people who live in the future matter morally just as much as those of us who are alive today.11 When we ask ourselves what we should do to make the world a better place, a longtermist does not only consider what we can do to help those around us right now, but also what we can do for those who come after us. The main point of this text – that humanity’s potential future is vast – matters greatly to longtermists. The key moral question of longtermism is ‘what can we do to improve the world’s long-term prospects?’.