Commissioned officers derive authority directly from a sovereign power and, as such, hold a commission charging them with the duties and responsibilities of a specific office or position. Commissioned officers are typically the only persons, in a military environment, able to act as the commanding officer (according to the most technical definition of the word) of a military unit.
Non-commissioned officers (NCOs) in positions of authority can be said to have control or charge rather than command per se, although the use of the word "command" to describe any use of authority is widespread and often official.
Having officers is one requirement for combatant status under the laws of war, though these officers need not have obtained an official commission or warrant. In such case, those persons holding offices of responsibility within the organization are deemed to be the officers, and the presence of these officers connotes a level of organization sufficient to designate a group as being combatant.
The Australian Defence Force, the British Armed Forces, the Pakistan Army and Navy (though not airforce), the Swiss Army, the Israel Defense Forces and the New Zealand Defence Force are different in not requiring a university degree for commissioning. They emphasise military, technical and leadership training and skills over academic qualifications, although a majority of officers in these militaries are now graduates. In the Pakistani Army all officers are by definition graduates, since officer training is recognized as the equivalent of a bachelor's degree.
In the U.S. military, officers without a university degree may under certain circumstances be commissioned, but are required to earn one within a time limit. A member of the U.S. armed forces may be selected for and graduate from the Officer Candidate School (OCS). The Army Officer Candidate School in particular is maintained to facilitate rapid expansion of the Army officer corps in the event of war, and commissions approximately 700 second lieutenants each year during peacetime. Another route to becoming a commissioned officer is through direct commission. Graduates from the service academies are commissioned immediately upon graduation; credentialed civilian professionals such as scientists, nurses, doctors and lawyers are also directly commissioned upon entry into the military or another federal uniformed service.
In countries whose ranking systems are based upon the models of the British Armed Forces, officers from the rank of Second Lieutenant (Army), Sub-Lieutenant (Navy) or Pilot Officer (Air Force) to the rank of General (Army), Admiral (Navy) or Air Chief Marshal (Air Force) are holders of a commission granted to them by the awarding authority. In Britain and other Commonwealth realms, the awarding authority is the British monarch (or a Governor General representing the monarch) as head of state. The head of state often is granted the power to award commissions, or has commissions awarded in his or her name.
In the United Kingdom, officers are commissioned both from the ranks and directly into the officer corps as what are known as 'Direct Entry' or DE officers, and commissioned from the ranks as 'Late Entry' or LE officers. LE officers, whilst holding the same Queen's Commission, generally work in different roles to the DE officers. In the infantry a limited number of Warrant Officers - Class 1 are commissioned as LE officers, ensuring that British infantry LE officers are in the top 1% of their peers. DE Officers require Secondary Education to A-Level standard and generally speaking 80% of officers have a degree. Commissioning for DE officers occurs after a 1 year course at the Royal Military Academy Sandhurst, or for Royal Navy and Royal Air Force candidates, an equivalent period at either Britannia Royal Naval College or the RAF College Cranwell respectively. Royal Marines Officers receive their training in the Command Wing of the Commando Training Centre Royal Marines. The courses consist of not only tactical and combat training, but also leadership, management and international affairs training.
By contrast, non-commissioned members rise from the lowest ranks in most nations. Education standards—a high school diploma or GED—for non-commissioned members are typically lower than for officers (with the exception of specialised-military and highly-technical trades). Enlisted members only receive leadership training as they are promoted to positions of responsibility, or as a prerequisite for such. In the past (and in some countries today but to a lesser extent) non-commissioned members were almost exclusively conscripts, whereas officers were volunteers.
In Commonwealth nations, Commissioned Officers are given commissioning scrolls (a.k.a. commissioning scripts) signed by the Sovereign or the Governor General acting on the monarch's behalf. Upon receipt, this is an official legal document that binds the mentioned officer to the commitment stated on the scroll.
In most maritime forces (navies and coast guards), the NCO ranks are called Petty Officers and Chief Petty Officers (Chiefs), with enlisted ranks prior to attaining NCO/petty officer status typically being called Seaman, or some derivation thereof. In most traditional infantry, Marine and air forces, the NCO ranks are known as Sergeants and Corporals, with non-NCO enlisted ranks referred to as Privates and Aircraftsmen in the case of the UK.
But some countries, including South Korea, are using the term of commission in order to describe the promotion of enlisted soldiers. Especially, in countries with mandatory military service, NCOs are referred to professional soldiers but not officers.