Company Sergeant Major (CSM) is the senior non-commissioned soldier of a company, responsible for standards and discipline. In combat, his prime responsibility is the supply of ammunition to the company. He also oversees the distribution of other supplies such as water or food (although that responsibility lies mainly with the Company Quartermaster Sergeant (CQMS)), as well as the evacuation of wounded and collection of prisoners of war.
For military units of the same level as company, the equivalent may be the Squadron Sergeant Major (SSM) or Battery Sergeant Major (BSM). In the Household Cavalry, the Squadron Corporal Major (SCM) is the equivalent. First Sergeant and Hauptfeldwebel are the United States Army and German equivalents respectively..
Canadian Forces
In the Canadian Forces, the CSM appointment is held by a Master Warrant Officer (MWO).
In the Canadian Forces, the SSM/BSM/CSM is referred to as "Sir" by subordinates, or as "Sergeant Major". Superiors refer to him generally as "Sergeant Major" or "CSM".
Singapore
In the Singapore Armed Forces, the CSM appointment is usually held by a staff sergeant or master sergeant. In the company, he may be addressed "CSM" by superiors, and "sergeant major" by subordinates. The CSM is often respectfully addressed "encik", Malay for "uncle", but the permission for junior enlisted men to do so may not be taken for granted.
United Kingdom
In the United Kingdom, the CSM is an appointment held by Warrant Officers Class 2 (WO2) in the British Army and Royal Marines, and also in other armies of the Commonwealth;
A CSM, BSM or SSM is generally addressed as "Sergeant Major" (or often as "Sir" or "Ma'am" by subordinates). However, a cavalry SSM is often addressed as "Mr (surname)" by officers, and as "Mr (surname), Sir" by his subordinates, with the salutation "Sergeant Major" being reserved for Staff Sergeants. Typically for the British Army, protocol can vary widely between units, creating a minefield for outsiders, new recruits, and soldiers serving outside their parent regiments.
The most famous fictional example is perhaps Battery Sergeant Major Tudor Brynne 'Shut Up' Williams, portrayed by Windsor Davies in the 1970s sitcom It Ain't Half Hot Mum.