This chapter will examine theatre both for, and by, the armed services on the fighting fronts. It will outline how and why theatre was an important aspect of leisure time for British, Colonial and allied troops fighting on land, at sea and in the air. This chapter will examine the importance of both watching and taking part in theatrical entertainments through a discussion of the professional civilian and military Concert Parties in the Army, Navy and the RFC/RAF, the role of voluntary-aid organisations such as the British Red Cross and the YMCA, and theatrical entertainments in wider wartime contexts such as PoW camps and military hospitals. A key focus of the chapter will be the social function of such entertainments, the content, and the practicalities of how they were staged in various wartime contexts.