Contrary to what could be believed, the variety of birds living in cities has very much increased over the century and continues to do so. The city offers a rich diversity of milieux which are hosts to varied species, often of rather unexpected origin. They belong to the category of forest birds, but also to rock or aquatic birds. City birds have modified their habits as regards nesting, eating, and the company of man. However they are threatened by pollution and also by the desire of modern life to live in a “perfect” world, clean, without insects or weeds. Individual initiatives, urban public policies and citizen’s movements try to put up with these threats.