Should you care less about your distant future? What about events in your life that have already happened? How should the passage of time affect your planning and assessment of your life? Most of us think it is irrational to ignore the future but harmless to dismiss the past. But this book argues that rationality requires temporal neutrality. It draws substantially from work in the history of philosophy, economics, and social psychology. It is written in a lively and approachable way, using many real case studies of planning puzzles ranging from retirement saving to cryogenic brain freezing. It should be of interest to anyone curious about theories of rationality, the role time plays in our preferences, and the nature of personal identity.