Motorized infantry is infantry that is transported by trucks or other motor vehicles. It is distinguished from mechanized infantry, which is carried in armoured personnel carriers or infantry fighting vehicles, and from light infantry, which can typically operate independently from supporting elements and vehicles for relatively long periods and may be airborne.

As defined by the United States Army, motorization is "the use of unarmored wheeled vehicles for the transportation of combat units." Motorizing infantry is the first stage towards the mechanization of an army. Civilian trucks are often readily adaptable to military uses of transporting soldiers, towing guns, and carrying equipment and supplies. Motorization greatly increases the strategic mobility of infantry units, which would otherwise rely on marches or railroads. In practice, armies have found it advantageous to develop trucks to military specifications, such as all-wheel drive, to have vehicles that function reliably in extremes of weather and terrain.

Motorization provides no direct tactical advantage in small-unit combat, as trucks and light utility vehicles are vulnerable to artillery and small arms fire. However, in larger battles, motorized infantry has an advantage in mobility allowing them to move to critical sectors of the battlefield faster, allowing better response to enemy movements, and the ability to outmaneuver the enemy.

The disadvantage of motorization is that fuel is critical; if motorized divisions run out of fuel, they may be required to abandon their vehicles.

The First World War was the first major war to see use of petroleum-powered vehicles used to transport supplies and personnel, and to fight the enemy. Unarmored and armored cars were dispatched to attack enemy positions and trains, and were used to patrol the front. However, this was on a small scale and a majority of movement was on foot and logistics with trains and horse-drawn logistics.

The Pancho Villa Expedition was a notable use of the armored car by the United States Cavalry under the command of General Pershing. There a Lieutenant George S. Patton was introduced to mechanized warfare when he led a small group of men against Villa's forces at San Miguelito Ranch.

After the war, the major militaries of the world saw the great benefit that motorized vehicles could have on the logistics and combat effectiveness of their infantry units.

In the 1920s, the British created the Experimental Mechanized Force between the wars to test the capabilities of all-arms formations of mechanized units, this included motorized infantry ("Motor Battalions").