The civil service is a collective term for a sector of government composed mainly of career civil servants hired rather than appointed or elected, whose institutional tenure typically survives transitions of political leadership. A civil servant, also known as a public servant, is a person employed in the public sector by a government department or agency for public sector undertakings. Civil servants work for central and state governments, and answer to the government, not a political party.

The extent of civil servants of a state as part of the "civil service" varies from country to country. In the United Kingdom (UK), for instance, only Crown (national government) employees are referred to as "civil servants" whereas employees of local authorities (counties, cities and similar administrations) are generally referred to as "local government civil service officers", who are considered public servants but not civil servants. Thus, in the UK, a civil servant is a public servant but a public servant is not necessarily a civil servant.

The study of the civil service is a part of the field of public service (and in some countries there is no distinction between the two). Staff members in "non-departmental public bodies" (sometimes called "QUANGOs") may also be classed as civil servants for the purpose of statistics and possibly for their terms and conditions. Collectively a state's civil servants form its civil service or public service. The concept arose in China and modern civil service developed in Britain in the 18th century.

An international civil servant or international staff member is a civilian employee who is employed by an intergovernmental organization. These international civil servants do not resort under any national legislation (from which they have immunity of jurisdiction) but are governed by internal staff regulations. All disputes related to international civil service are brought before special tribunals created by these international organizations such as, for instance, the Administrative Tribunal of the ILO. Specific referral can be made to the International Civil Service Commission (ICSC) of the United Nations, an independent expert body established by the United Nations General Assembly. Its mandate is to regulate and coordinate the conditions of service of staff in the United Nations common system, while promoting and maintaining high standards in the international civil service.