Is the world at an historical threshold, where we risk dooming ourselves and our planet if we don't change the way we exploit the earth's resources? Or are environmentalists being alarmist, underestimating nature's resilience and humanity's adaptiveness? These and other questions are discussed by environmentalist Norman Myers, and Julian Simon, an economist and outspoken sceptic on environmentalism. This book is a transcript of their provocative exchange in a debate held at Columbia University in October 1992. The authors also provide position statements and replies that let readers judge for themselves whose arguments are more persuasive.