The Willow Flycatcher (Empidonax traillii) is a small insect-eating bird of the tyrant flycatcher family.

Adults have brown-olive upperparts, darker on the wings and tail, with whitish underparts; they have an indistinct white eye ring, white wing bars and a small bill. The breast is washed with olive-grey. The upper part of the bill is grey; the lower part is orangish. At one time, this bird and the Alder Flycatcher were considered to be a single species, Traill's Flycatcher.

Their breeding habitat is deciduous thickets, especially willows and often near water, across the United States and southern Canada. They make a cup nest in a vertical fork in a shrub or tree.

These birds migrate to Mexico and Central America, often selecting winter habitat near water.

They wait on a perch near the top of a shrub and fly out to catch insects in flight, also sometimes picking insects from foliage while hovering. They may eat some berries.

This bird's song is a sneezed fitz-bew. The call is a dry whit.