The tyrant flycatchers (Tyrannidae) are a clade of passerine birds which occur throughout North and South America. They are considered the largest family of birds, with more than 400 species. They are the most diverse avian family in every country in the Americas, except for the United States and Canada. As could be expected from a family this large, the members vary greatly in shape, patterns, size and colors. Some tyrant flycatchers superficially resemble the Old World flycatchers which they are named after but are not related to.