Although flight is often considered one of the most salient characteristics of birds, in the course of their evolution, various avian lineages have lost the ability to fly. This books explores various aspects of the multifaceted evolutionary processes that have led to loss of flight in several groups of birds. The nine papers in this collection deal with flightless birds belonging to widely different extinct and extant groups, from many parts of the world and from various time periods, from the Late Cretaceous to the Quaternary. They illustrate both the diversity of flightless birds and the multifarious approaches that can be used to study them, from stratigraphy and functional anatomy to phylogenetic analysis and bone histology.