A drill sergeant drills recruits in the U.S. Army.

A Drill Instructor or Drill Sergeant (DI or DS) is a non-commissioned officer in the military who is assigned the duty of initiating new recruits entering the military into the customs and practices of military life.

The drill instructor's responsibilities usually include instilling military discipline, improving recruits' physical fitness, and initial weapons training.

Drill Instructors in the United States Marine Corps and Drill Sergeants in the United States Army normally hold the rank of staff sergeant or sergeant first class and are held responsible for the welfare, behavior and military education of the recruits assigned to them on a twenty-four-hour basis throughout the period of initial training, popularly known as boot camp.

Because of the extremely demanding nature of this duty, drill instructor assignments are regarded as among the most arduous and the most prestigious carried out by enlisted military personnel. Those who become drill instructors are eligable for a variety of military awards, such as the Drill Instructor Ribbon and Drill Sergeant Identification Badge.