It is a known fact that a majority of the world’s population is now living in cities, and most of the fastest expanding megacities are in the hot regions of the world. Developing countries and their cities have, at present, lower energy use and climate emissions, but this is changing fast. This book addresses cities where the main energy requirement—and source of unwanted urban heat—is for cooling. Our discussion is also relevant in many other contexts, such as cities where there is a need for both summer cooling and winter heating, and indeed, in many temperate climate cities, even in northern Europe, there is a growing need for cooling too—due partly to poor building design such as with excessive glazing. Principles for climate-responsive building design and for sustainable city planning are well known, including from long traditions, but are still seldom applied. However, the urban heat island effect is becoming a very major issue both for energy use and climate emissions, as well as increasing mortality. This is also an issue of equity since it is the poor who are most exposed to heat events. Designing cooler environments is one of the major challenges faced by cities with hot climate. This chapter provides a brief overview of energy and cooling in cities and notes the principal design approaches. It also introduces questions raised by contributing authors in subsequent chapters of the book.