The 166th Aviation Brigade is an aviation training brigade of the United States Army headquartered at Fort Cavazos, Texas. It was a subordinate unit of First Army – Division West. An "AC/RC" formation, the 166th Aviation Brigade was the sole organization responsible for the post-mobilization training of United States Army Reserve & National Guard aviation units. The unit was formerly designated as 3rd Brigade, 75th Division.

First Army is the oldest and longest-established field army of the United States Army. It served as a theater army, having seen service in both World War I and World War II, and supplied the US army with soldiers and equipment during the Korean War and the Vietnam War under some of the most famous and distinguished officers of the U.S. Army. It now serves as a mobilization, readiness and training command.