The olive-sided flycatcher is a small to medium sized passerine bird in the family Tyrannidae, the tyrant flycatcher family. It is a migratory species that travels from South America to North America to breed during the summer. It is an agile flyer and mainly consumes flying insects caught in flight. Since 2016, this species has been assessed as being near-threatened globally (IUCN) and threatened in Canada (SRA) due to its declining populations.