While Executive officer literally refers to a person responsible for the performance of duties involved in running an organization, the exact meaning of the role is highly variable, depending on the organization.

In many militaries, an Executive Officer (XO) is the second-in-command, reporting to the Commanding Officer (CO). The XO is typically responsible for the management of day-to-day activities, freeing the commander to concentrate on planning the unit's next move. The XO also takes charge in the absence of the commander, and the position is frequently a stepping stone to a command position. The term is not used in the British Army, in which the designation Second-in-Command (2i/c) is used as a formal appointment. In smaller ships of the Royal Navy (such as submarines and frigates), the Executive Officer also holds the position of First Lieutenant and is usually referred to as such. In larger ships, in which he holds the rank of Commander, he is usually referred to simply as "the Commander". The XO heads the Executive Department.

In business, the executive officers are the top officers of a corporation, the chief executive officer (CEO) being the best-known type. The definition varies; for instance, the California Corporate Disclosure Act defines "executive officers" as the five most highly-compensated officers not also sitting on the board of directors.

In government, "executive officer" may be anyone with decision-making responsibility in the executive branch of the government.