| Bull Run | |
| Name Other: | Tributary to Occoquan River |
| Map Size: | 300 |
| Pushpin Map: | USA Virginia#USA |
| Pushpin Map Size: | 300 |
| Pushpin Map Caption: | Location of Bull Run mouth |
| Pushpin Map Alt: | Map of Bull Run mouth location |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Virginia |
| Subdivision Type3: | County |
| Subdivision Name3: | Fairfax Prince William Loudoun |
| Length: | 31.8miles[1] |
| Discharge1 Location: | Occoquan River |
| Discharge1 Avg: | 229.13cuft/s at mouth with Occoquan River[2] |
| Source1: | Hungry Run divide[3] |
| Source1 Location: | Cold Spring Gap |
| Source1 Coordinates: | 38.9392°N -77.6531°W[4] |
| Source1 Elevation: | 660feet |
| Mouth: | Occoquan River |
| Mouth Location: | about 1 mile northeast of Ravenwood, Virginia |
| Mouth Coordinates: | 38.7225°N -77.3808°W |
| Mouth Elevation: | 120feet |
| Progression: | southeast |
| River System: | Potomac River |
| Tributaries Left: | Foley Branch, Cub Run, Little Rocky Run, Johnny Moore Creek, Popes Head Creek, Old Mill Branch |
| Tributaries Right: | Black Branch, Chestnut Lick, Bull Run tributary, Little Bull Run, Youngs Branch, Holkums Branch, Flat Branch, Russia Branch, Buckhall Branch |
| Bridges: | Loudoun Drive, New Road, US 15, Peach Orchard Lane, Auburn Farm Road, Gum Spring Road, US 29, I-66, Old Centerville Road, VA 28, VA 612 |
Bull Run is a 31.8adj=midNaNadj=mid[5] tributary of the Occoquan River that originates from a spring in the Bull Run Mountains in Loudoun County, Virginia, and flows south to the Occoquan River. Bull Run serves as the boundary between Loudoun County and Prince William County, and between Fairfax County and Prince William County.
Bull Run is primarily associated with two battles of the American Civil War: the First Battle of Bull Run (July 21, 1861) and the Second Battle of Bull Run (August 28–30, 1862), both Confederate victories. A narrow part of the creek called Yates Ford (near Manassas) is the scene of the Battle of Occoquan, and downstream about one mile is the current Yates Ford Road bridge between Fairfax and Prince William counties.