From the Preface: The chapters of this book contain contributions from an international group of specialists. They address some important themes in both modern and ancient reef systems. Some chapters contain `snapshots' of reefs of particular intervals, while others touch on relevant themes of both modern and ancient reefs - themes that weave their way through reefs of all ages. This book opens and sets the stage with an introduction to both modern and ancient reefs and reef ecosystems. This chapter is also intended as a basic introduction for students, general geologists, and professionals or others who may be unfamiliar with reefs and reef ecosystems. The chapter addresses the living coral reef ecosystem, stressing among other relevant factors, the importance of ecological and physical interactions between the organisms and their environment. The chapter also addresses mass extinction and provides a general overview of the history of reefs.