We have come a long way towards better understanding how new species originate, i.e. speciation, which long remained Darwins mystery of mysteries. Since speciation is the underlying mechanism for radiations, it is the ultimate causation for the biological diversity of life that surrounds us. Without a doubt, Charles Darwins contribution to our understanding of the origin of biodiversity cannot be overestimated. This book is a contribution to both the Darwin Year we celebrated in 2009 and to the Year of Biodiversity and Conservation 2010. The studies and model cases presented show the progress and dynamics of research based on Darwinian theories and sheds light on its implications in the context of current biodiversity crises. The great importance of adaptive (and non-adaptive) radiations for biodiversity is widely accepted, but our understanding of the processes and mechanisms involved is still limited and generalizations need to be based on the accumulation of more evidence from additional case studies. The studies presented in this volume are those urgently needed and focus on a variety of organisms and different aspects of radiations. The scientific results presented therein are excellent examples not only of evolution in action, but also of active research on evolutionary processes and their most apparent outcome biodiversity.