When we asked our colleagues to list what they consider the most pressing problems facing our planet today, they came back with a wide range of concerns, including atmospheric pollution, climate change, intensifying security threats, and the need to secure an adequate food supply for all the world’s people. Given that we concentrate in this book on the most crucial of these issues, it is dispiriting that we should still have to begin with the most basic of human needs. In the early twenty-first century, a lack of food, water, and shelter continues to rob tens of millions of people of their lives every year. More than half of all the world’s deaths are attributable to malnutrition. More people die of hunger every year than perished in the whole of World War II. What makes this problem especially distressing is that we know it isn’t necessary. That’s why we give particular prominence in this book to the question of what we should do about it. Once the basic necessities have been taken care of, the next biggest killers are cancer and infectious diseases. And as we grow older, we become increasingly concerned about our reliance on caregivers and the decline in our cognition. Breakthroughs in these fields would enable us to live longer and happier. So that’s the second category of challenges we discuss in this book. The continued existence of the human race is not, of course, guaranteed. The rapid pace of change on our planet requires us to adapt significantly and quickly. We discuss the issues arising from that recognition in a separate part of the book devoted to the sustainability of our Earth. The stability of our society isn’t guaranteed either. Financial crises, explosive urban growth, and armed conflict all have a detrimental effect on our well-being, making this the fourth category of the problems we consider. In our view, the most important issues human beings need to work on are: malnutrition, drought, cancer, infectious diseases, care of the elderly, cognitive deterioration, climate change, depletion of natural resources, natural disasters, educational deprivation, habitable cities, financial instability, war and terrorism, and the infringement on personal integrity.