Species diversity is an index that incorporates the number of species in an area and also their relative abundance. Since species diversity is central to a large amount of ecological theory, its accurate measurement is key to understanding community structure and dynamics. Consequently, during the course of evolution, species have always gone extinct; however, the rate of extinction has increased in recent decades by as much as one hundred fold, some owing to environmental impact, mainly due to human activities. The authors of this book present and review important data on biodiversity and species extinction.