The 43rd Virginia Cavalry Battalion, also known as 43rd Virginia Rangers, Mosby's Rangers, Mosby's Raiders, or Mosby's Men, was a battalion of partisan cavalry in the Confederate Army during the American Civil War. Noted for their lightning strike raids on Union targets and their ability to consistently elude pursuit, the Rangers disrupted Union communications and supply lines.

The 43rd Battalion was formed on June 10, 1863 at Rector's Cross Roads, near Rectortown, Virginia, when John S. Mosby formed Company A of the battalion. He was acting under the authority of General Robert E. Lee, who had granted him permission to raise a company in January 1863 under the Partisan Ranger Act of 1862 in which the Confederate Congress authorized the formation of such units. By the summer of 1864, Mosby's battalion had grown to six cavalry companies and one artillery company, comprising about 400 men. After February 1864, the Confederate Congress revoked the authority of all partisan units, except for two, one of which was the 43rd Battalion, the other being McNeill's Rangers. The battalion never formally surrendered, but was disbanded on April 21, 1865, after Lee surrendered the Army of Northern Virginia at Appomattox Court House to Ulysses S. Grant but not before it had attempted to negotiate surrender with Major General Winfield S. Hancock in Millwood, Virginia.

What to call the Confederate 43rd Battalion was a matter of contention during the war. The members of the battalion were referred to as soldiers, partisans, rangers, and guerillas.

The Union viewed them as unsoldierly: a loose band of roving thieves. Northern newspapers and Unionists referred to them as guerrillas, a term of opprobrium at the time. One of Mosby's men, Munson stated in memoirs published after the war that "the term [guerrilla] was not applied to us in the South in any general way until after the war, when we had made the name glorious, and in time we became as indifferent to it as the whole South to the word Rebel."

Mosby himself avoided overtly militaristic words like "troops" or "soldiers" or "battalion" in favor of the more familial "Mosby's Men" or "Mosby's command".

The method of operation involved executing small raids with up to 150 men (but usually 20 to 80) behind Union lines by entering the objective area undetected, quickly executing their mission, and then rapidly withdrawing, dispersing the troops among local Southern sympathizers, and melting into the countryside.

Mosby's area of operations was Northern Virginia from the Shenandoah Valley to the west, along the Potomac River to Alexandria to the east, bounded on the south by the Rappahannock River, with most of his operations centered in or near Fauquier and Loudoun counties, in an area known as "Mosby's Confederacy". Mosby's command operated mainly within the distance a horse could travel in a day's hard riding, approximately 25 miles (40 km) in any direction from Middleburg, Virginia. They also performed raids in Maryland.

Of his purpose in raiding behind the Union lines, Mosby said: