The company sergeant major (CSM) is the senior non-commissioned soldier of a company in the armies of many Commonwealth countries, responsible for administration, standards and discipline. In combat, their prime responsibility is the supply of ammunition to the company. They also oversee the distribution of other supplies, such as water or food, although that responsibility is mainly that of the company quartermaster sergeant (CQMS), and evacuating the wounded and collecting prisoners of war.

A company is a military unit, typically consisting of 100–250 soldiers and usually commanded by a major or a captain. Most companies are formed of three to seven platoons, although the exact number may vary by country, unit type, and structure.