Favored theories of the derivation of the term relate to the Relic Cloak (capa or capella) of St. Martin of Tours or from the Latin term Capellanus.
In various languages, the word equivalent to Almoner (e.g. Aumonier in French, Aalmoezenier in Dutch) is used in many instances where English uses chaplain, sometimes there are still other terms (e.g. also Proost, otherwise equivalent to Provost, in Dutch).
In the Old Testament book of Joshua, Levite priests accompany the Israelites' military and political expedition into Israel; carrying the Ark of the Covenant and playing a major role in the goodwill of military matters. While these priests cannot be considered "chaplains" with the current meaning, their role as spiritual aides provides a model for modern chaplains to rely upon.
Originally a Christian chaplain had a function of serving as an aide to a Bishop and various chaplains still help the Pope in his ecclesiastical duties. In other circumstances their duties were limited to saying a Mass in certain functions. In many catholic parishes the curate has (or had, manpower is usually to low for such luxury) one or more younger priests, styled Chaplains, attached to him, under his ordinary jurisdiction.
As in feudal times most laymen, for centuries even most noblemen, were poorly or not educated, this literate clergy was often employed as advisers and secretarial staff (as in a Chancery) until the advent of legists and proper bureaucratic civil service (mainly under Absolutism), hence the term clerk derived from Latin clericus ('clergyman'), making them very influential in temporal affairs as well the moral impact as hearing the confession of the elite.
The current form of military chaplain dates from the era of the First World War. A chaplain conducts religious services in the field and tries to maintain Morale. In the British Armed Forces, chaplains are traditionally referred to (and addressed) as padres.
Christianity is not the only faith to have chaplain-equivalent positions. Other religions, such as Judaism or Islam, may also provide chaplains for military service. In the United States Air Force, the Air Force Religious Pin recognizes chaplains from four of the major religious faiths. The British Armed Forces traditionally only employed Christian and Jewish chaplains; the appointment of chaplains from other faith groups occurred for the first time in October 2005.
Chaplains are nominated in different ways in different countries. A military chaplain can be an army-trained soldier with additional theological training or a priest nominated to the army by religious authorities. In Britain, the Ministry of Defence employs the chaplains but their authority comes from the church. In France, the existence of military chaplains has come under debate because of the Separation of church and state; however, their position has been maintained as of 2004.
In the United States, Catholic Priests are required to seek permission from their diocesean Bishop or religious superior to be released from parish or other diocesean work for at least three years. Candidates are given medical examinations to see if they would be healthy enough to serve. They are also required to fill out an application, and have letters of recommendation. The findings are presented to a board which evalulates each candidate. The application process usually takes from two to six months to complete.
Some Chaplains also break the Geneva Conventions and act as combatants, usually only if and when the situation warrants itself. Examples of this include such incidents as recorded by Chaplain (then Captain) James D. Johnson, of the 9th Infantry Division, Mobile Riverine Force in Vietnam. In his work Combat Chaplain: A Thirty-Year Vietnam Battle, Johnson explains his "unofficial training" with the M-16 assault rifle and Colt 1911 .45 caliber pistol, as well as carrying the M-16 while embedded with a combat patrol. While this is the exception rather than the rule, chaplains, like other noncombatants (including medics) have been recorded as breaking the Conventions under extenuating circumstances.
Many hospitals and hospices employ chaplains to assist with the spiritual needs of patients, families and staff. In the United States, healthcare chaplains are typically educated through the Association for Clinical Pastoral Education and may be certified by one of the following organizations: The Association of Professional Chaplains, The National Association of Catholic Chaplains, or The National Association of Jewish Chaplains. In Canada, they may be certified by the Canadian Association for Pastoral Practice and Education. Certification typically requires a Masters of Divinity degree, faith group ordination or commissioning, faith group endorsement, and four units (1600 hours) of Clinical Pastoral Education.
Even some large businesses employ chaplains for their staff and/or clientele. The National Institute of Business and Industrial Chaplains is one of the agencies that certify chaplains for business settings in the United States.