This species is extremely similar to the eastern wood-pewee and is best identified by range and voice. Vagrants should be identified with great care and preferably documented with recordings of vocalizations, photos, or video. This is the only exclusively western-breeding passerine that winters almost entirely in South America. Polytypic (5 ssp. north of Mexico). Length 6.3".

Adult: extremely similar to eastern wood-pewee, with long wings that extend one-third of the way down the tail. Average differences listed below, but plumage somewhat variable. western wood-pewee tends to be slightly darker, browner, and less greenish than eastern wood-pewee, with complete grayish breast band, darker centers to undertail coverts, less pale nape contrast, and duller back. Wing bars, on average, are narrower and