Ornithology is the scientific study of birds. It is perhaps the only discipline in zoology that has benefited greatly from the contributions of amateurs. Much has been learned about the distribution, migratory movements, and ecology of birds from the observations of amateurs and such observations by ordinary people often have the advantage of being completely unbiased. This dictionary has been prepared as an aid for bird enthusiasts seeking definitions for unfamiliar terms or bird names that they may encounter in ornithological literature. It is a much enlarged and enhanced version of the author''s earlier work, A Dictionary of Ornithological Terms. Apart from technical and colloquial (informal) terms related to ornithology and birding, this dictionary also lists all the species in each genus and all genera in each family of birds. Thus, it will be a valuable source of reference for birders when they want to find out scientific names of birds or when a scientific name is given, its common name. Altogether, there are over 15,500 entries.