In the fall of 2006, I received a phone call from Charles (Chuck) Harper, then the Senior Vice President and Chief Strategist of the John Templeton Foundation (JTF). Chuck asked me, What are the topics that most need attention in your field (philosophy of physics) but that are not receiving funding from other sources? I told Chuck that current academic culture does not provide much encouragement for scientists to pursue “foundational” or “philosophical” issues. Whereas in previous centuries many of the great scientific minds also displayed a sharp philosophical acumen—witness Descartes, Leibniz, Bohr, Einstein, von Neumann, and Weyl—our current generation of great scientists seems to lack the time, ability, or interest to expand their scientific research into the more speculative or conceptual realms. So I told Chuck we should provide some encouragement to those scientists who wish to continue the tradition of philosophical reflection on their subjects. This book is the direct result of Chuck’s, and JTF’s, taking this idea seriously—that is, the idea that “philosophical” is not an antonym of “scientific.” Concretely, the support provided by JTF enabled us to bring a group of distinguished philosophers and scientists from around the globe to Princeton, New Jersey, for a two-day conference in October 2007. The invited speakers were given free rein to speak on whatever topic they chose.