From the earliest days of conflict, leaders had staff assistants, if only to hand them the next rock to throw at the mammoth. As man's ability to kill grew, so did the need for assistance to leaders. Still, for centuries, a military staff was organized around an individual, rather than in a systematic way.
One of the challenges of discussing the development of modern staff concepts is separating them from operational warfare, as true staffs emerged at roughly the same time as the corps level of organization, historically the first level that could force battle to be conducted at a particular place, time, and set of condition. While the technology of current units can put the operational role at a considerably lower level, the challenge remains. Contemporary histories tend, for example, to intermix accounts of Napoleon's use of corps with his use of a staff.
A sub-article discusses the historical development of military staffs.
This article goes into examples of current staff organizations, including the European Union's Eurocorps and the U.S. Restructuring of the United States Army. A trend in these organizations is to assign considerable resources for the direct support of staff functions, especially intelligence and information operations.
A staff exists to give battlefield awareness to the commander:
Knowledge and understanding of the operational area’s environment,
factors, and conditions, to include the status of friendly and adversary forces, neutrals and noncombatants, weather and terrain, that enables timely, relevant, comprehensive, and accurate assessments, in order to successfully apply combat power, protect the force, and/
or complete the mission
The concept of a formal "chief of staff" is rarely present until a unit is led by a general officer (i.e., division-equivalent or above). Below that, the "S" organization reports to the commanding officer. Several militaries, including those of Russia and the U.S., had assistants that coordinated subgroups of the staff. In the U.S. Army, the executive officer typically was responsible for personnel and logistics (and civil affairs if present); the Soviet/Russian equivalent went by several names, but "chief of the rear" was representative. The operations officer, however, has his own section, but also oversees intelligence and communications-electronics.
General vs. special staff
All staff officers having duties at a headquarters and not included in the general (coordinating) staff group or in the personal staff group. The special staff includes certain technical specialists and heads of services, e.g., quartermaster officer, antiaircraft officer, transportation officer, etc. 
"Head of service" means the individual may be "dual-hatted" as a special staff officer and as the highest level commander of a group of units. In U.S. practice, the Command Surgeon both has a staff function but also commands all medical units in the organization.
Eurocorps' Engineer both advises the staff on military engineering, but commands the engineer units.  In the U.S. V Corps in Europe, the Engineer staff section is G-8, but is a coordination rather than command organization.  Note that while the Engineer would normally be considered special staff, the G-8 is an Assistant Corps Engineer and part of the Corps General Staff. In a U.S. command, staff branches 1-4 and 6 are fairly predictable, but there can be many alternative structures.
Levels of staff
Subdivisions of a staff are usually identified by a letter and number. The letter indicates the level of organization with which the staff is associated. While the boundaries of a level may vary, common NATO levels are:
- S: Battalion through brigade
- G: Division through army; assumes a single military service
- J: Joint command, containing elements from multiple services
- C: Coalition command, with elements from different countries
Traditional divisions of a staff
In the U.S., NATO, and a number of countries, major staff divisions are given a letter-number designation, where the level identifies the hierarchical position of the unit to which the staff belongs, and the number indicates the function. Especially in larger staffs, there may be prefixes for sections of the divisions.
- S: Battalion, regiment, brigade
- G: Division, corps, and army; a single military service
- J: (Joint) organizations with components from multiple services (i.e., ground, sea, air) of a single country
- C: (Combined) organizations involving multiple countries
While not strictly a staff division, each headquarters and command post needs a "housekeeping" unit for local support ranging from electrical power, to site preparation and building/shelter setup, to food service, etc.
Division 1: Personnel and administration
This branch is responsible for tracking the number and status of personnel in the unit, replacing or augmenting manpower, individual training, awards and decorations, etc.
Division 2: Intelligence (and security)
An intelligence staff both produces analyses and other reports, and frequently has intelligence collection units reporting to it. While a battalion-level S-2 intelligence section may consist only of an intelligence officer and an intelligence sergeant, the higher in the command hierarchy in which this branch appears, the more likely it is that it will have sections for the major parts of the intelligence cycle:
- Collection and processing
In highly technical militaries, there is a trend to have more and more collection capability in lower-level units, since lower-level units are more likely to fight operational warfare and thus need to do their own short-term collection. At a minimum, the intelligence branch has operational control of reconnaissance/scouting units. Such units historically have been specialist ground troops, but there is a strong tendency to have, at a minimum, an unmanned aerial vehicle aerial reconnaissance capability to provide imagery intelligence. The branch frequently will control at least a basic signals intelligence capability, which, at least, has direction finding, security monitoring of one's own communications, operation of secure communications to higher-level intelligence, and HUMINT/counterintelligence specialists.
It will participate in an intelligence collection planning process, with higher-echelon intelligence units, to determine which unit and technology will cover which aspects of the enemy. As with Eurocorps, there may be an explicit planning cell.
Even if G-3 controls the situation map, G-2 is responsible for the information on that map that pertains to enemy forces. The intelligence branch will present frequent and periodic summaries of enemy force status, and, where appropriate, movements and intentions.
In a combat organization, the intelligence branch is most likely to handle material within compartmented control systems, and thus it is a logical place for the Special Security Office(r), responsible for such information, and, if the headquarters needs one, a Sensitive Compartmented Information Facility (SCIF). The SCIF will contain intelligence communications systems (e.g., JWICS), and be restricted to staff cleared for SCI; the U.S. slang term for the operations in a SCIF is "behind the green door".
Counterintelligence and human intelligence
Clandestine human-source intelligence, complementing the less sensitive prisoner interrogation and other human-source intelligence functions, is apt to be one of these sensitive areas. In U.S. doctrine, there will be HUMINT control function identified by an "X" suffix to the C/J/G-2 level (e.g., G-2X) and a HUMINT operations cell (HOC) at brigade and above, and an Operational Management Team at battalion.
Brigade Combat Teams
U.S. Brigade Combat Teamss (BCT) now contains both a Military Intelligence (MI) company and an Reconnaissance, Surveillance and Target Acquisition Squadron (RSTA) Squadron, all reporting to S-2, with information distribution through such things as Force XXI Battle Command, Brigade and Below system (FBCB2), These assets will increase situational awareness in both the BCT and other units. Every vehicle and dismounted soldier outfitted with it becomes a collector and can report information digitally. The S-2 function adds the function of intelligence analysis to the surveillance and reconnaissance roles, such that its mission is described as ISR (intelligence, surveillance and reconnaissance).
Special Forces units may be augmented with two-man HUMINT/CI teams. Cite error: Invalid
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Divsion 3: Operations
Responsible for unit, as opposed to individual training, and the mobilization and deployment of units for combat. Ground units frequently have a deputy for air support.
As opposed to a Plans and Policy staff division, which is typically the J-5 at a higher headquarters, G-3 plans is responsible for short-term operational procedures, guidance, and specific plans. These include: co-ordination of all operational short-term planning and all operational guidelines, manuals and Standard Operating *close, deep and rear operations by conventional forces.
- special operations
- information operations (IO). In Eurocorps, this is normally divided into a psychological operations and an information operations cell, while U.S. doctrine has psychological operations as a subgroup of IO
"The G3 Branch’s brains are tasked with foreseeing operations in the future and thinking over all possible ways of action within the very strict frame of order writing...The G3 Plans section manages the Decision-Making Process (DMP) and the Corps Battle Rhythm. The co-operation, co-ordination and liaison with the higher echelon, LNOs to the HQ EC, Air and Naval Component are conducted within G3 Plans.
G3 Training and Exercises
This branch prepares both command post and troop exercises, as well as budgeting for training and supervising the execution of exercises.
G-3 operations maintains the "big picture" for the commander and staff, and communicates status and actions within the Eurocorps headquarters, to subordinate units, and to external headquarters and organizations that need such information. It operates the Main and Alternate command post, and also manages alerting and mobilization. In Eurocorps, it is responsible for force protection through the Military Police Staff Officer/Force Protection Officer, while [[force The primary functions of G3 Operations are the maintenance and promulgation of a common operating picture, both within the headquarters and externally, and the conduct of the current battle. It contains:
- Alert & Mobilization cell
- Home Base Ops Centre cell
- OPSCEN cell
- Military Police & Force Protection cell.
G3 Fire Support Co-Ordination Centre
Two major areas fall under this branch, working closely with the G-3 Air. First, it is responsible for the overall coordination of land, air, and naval fires in support of maneuver. It also plans both lethal and non-lethal (e.g., information operations fires in support of operations, and does the targeting for those fires. The section is organised in the following sub-cells:
A good definition of fires
Fires are not limited only to strikes against fielded enemy units, but they encompass a broad spectrum of targets that attacks all of the enemy's centers of gravity such as: the enemy’s leadership; infrastructure and key production components (transportation, energy, command control communications computers and intelligence (C4I), nuclear biological and chemical (NBC, also known as weapons of mass destruction or WMD), theater ballistic missiles (TBMs) war-making industries and non-lethal methods targeted at the population. Effective joint fires produce effects beyond the proportion of effort expended in execution. Joint fires are long term efforts that have both immediate and long term effects on the enemy's capability and will to prosecute the war.
"The G3 is COMUSARCENT’s executive agent for Deep Operations, with a 96-hour planning cycle and 72-hour targeting cycle. All other ARCENT staff sections are responsible for coordinating Deep Operations actions with the G3. Within the G3 is the Deep Operations Division (DOCC)
- coordinates targeting guidance and objectives
- develops a candidate target list for integration with the air tasking order (ATO)
- monitors ATO execution
- fire support coordination measures.
The DOCC is divided into five branches:
- Deep Operations Branch consist of
- Target Development
- Operations [OPS]
The Operations Section (OPS) is responsible for battle management within the DOCC for ATOs which are 48 and 24 hours out from execution. This includes monitoring the development of the ATO, other planned deep operations, and coordinating the complementary actions required to support the land component commander guidance and intent.
- Prepare Air Interdiction (AI) divert list based on targeting guidance changes (24-48 hour time period)
- Integrate Theater Missile Defense (TMD) Attack Operations with deep battle operations
- Receive and parse the Air Tasking Order (ATO) / conduct ATO hand over briefing with the FSE
- Receive feedback from the BCD on LCC AI nominations submitted to the C/JFACC
- Assess the Commander’s guidance and objectives through the Combat Assessment Board
- Develop operational fires FRAGOs.
- Electronic Warfare (EW) Branch; attack and deconfliction
- Command and Control Warfare (C2W) Branch (i.e., information operations less PSYOP)
- PSYOP Branch;
- Fire Support Element (FSE): This is gthe current operations cell, which coordinates:"Based on the current **"diverts" (re-directing airborne aircraft from striking one target to striking another higher priority target), **"re-roles" (changing the mission (CAS, AI, etc) of airborne aircraft to attack a new set of targets).
- adjudicator of CAS allocations for subordinate ground forces which involves shifting assets as necessary to support the different MSC fights.
- Attack of Time Sensitive Targets (TSTs) is a FSE function. ...Attack of TSTs is solely driven by the asset that can service it in the most expedient manner, usually aircraft or ATACMS."
This staff section interfaces among the organic aviation and air defense units, as well as airspace management to deconflict aircraft and unmanned aerial vehicles from higher headquarters or the supporting Air Force components.
Division 4: Logistics
While the units under the control of G-2 may be small enough for direct reporting, the massive organizations needed for logistics may necessitate separating the logistics section of the staff from the logistics support command, which has its own staff, organized for its needs.  In Eurocorps, the logistics division of the main staff has the branches:
- G4 Operations: responsible for presentation of logistic situation to the Commanding General, and running the appropriate information sysetms. It also issues logistic orders and guidelines for subordinate units and tasks EC Log Corps troops.
- G4 Plans manages the whole planning, command and logistic policy. To check the relevance of the concepts and procedures created by the section, it regularly organizes or takes part in seminars to share information and ideas with other High Readiness Force HQs. In peacetime it is responsible for developing logistics-related concepts and SOPs.
- G4 Movement and Transport Section plans the detailed deployment plan for HQ Eurocorps and the Multinational Command Support Brigade from the garrison to the area of operations. It complements the operational and tactical movements under G-3,
- G4 Reception, Staging and Onwards Movements section develops the RSOM plans. It is responsible for co-ordinating the RSOM process of Eurocorps from the port of debarkation to the area of operations with the Troop Contributing Nations, the Host Nation and the superior headquarters including NATO HQs. In peacetime, it is responsible for developing the RSOM concept and related Standard Operating Procedures.
- G4 Medical is responsible for the planning and co-ordination of medical support throughout the Corps' area of operations. In Europcorps, the Chief of this section is the Medical Adviser (MEDAD) to the Commanding General. In the U.S., the unit Command Surgeon (i.e., senior medical officer) is also a member of the Commanding General's special staff. As with logistics staff versus logistic commands, medical services will usually have field and evacuation hospitals, public health specialists, etc. that are in the operational logistics organization rather than the main staff, although some specialists may be "dual-hatted".
Division 5: Plans and Policy
While "5" has, historically, contained civil affairs, that function increasingly moves to a branch of its own, under civil-military operations. In Eurocorps specifically, G-5 both plans Eurocorps operations, but also deals with higher headquarters and the constituent nations.
- G-5 Plans Section: planning of future operations. In peacetime however, it also contributes to the general specifications for exercises, participates in exercise planning conferences.
- G-5 Policy and Studies Section: This section turns the Commanding General's guidance and directives into Standing Operating Procedures, conducts ad hoc studies for the Command group and ensures a staff-wide co-ordination and integration of policy aspects into planning.
- G-5 Operational Analysis and Requirements (OPAR) Section: This section is responsible for the evaluation of the exercises in which Eurocorps is taking part. In operations, OPAR also prepares the Statements of Requirement and monitors the force generation process outside the top-level headquarters. This section records the lessons learned in exercises and disseminates them to those who can use them.
- G-5 International Relations Section: This section establishes and sustains relationships with NATO, other multinational HQs, the EC's Framework Nations and other Sending Nations, the UN, the OSCE and the European Union. While the section provides the EC's secretary for both POLMIL and MIL Group meetings, ACOS G5 and the members of the international relations section are the Commanding General's official representatives in these groups and represent the EC's official positions and interests.
Division 6: Communications-Electronics
A communications-electronics staff manages both the command & control information system (CCIS) and the tactical area communication system(s) for the unit of which it is part. In addition, it provides the engineering support for information and communications security programs appropriate for the unit and its area of operations.
The CCIS interconnects the various command posts (e.g., Forward, Rear, and Main) of its unit, as well has having connectivity to peer and higher headquarters. It allows access to national and coalition databases, at appropriate levels of classification and access control, and provides multimedia (e.g., video teleconferencing (VTC), image transfer, etc.) as well as message communications (e.g., email).
It works closely with the Operations part of the staff. In some units, the Operations Officer may have staff control of the Communications-Electronics branch. Frequency management is a very basic piece of communications operations, making sure that all units have primary and backup frequencies for communications with the units with which it operates, and that there is no duplication of frequency assignments that would cause conflict. It cooperates closely with the electronic warfare part of the operations branch, to make sure electronic attack does not damage friendly communications, and to define the emanations control (EMCON), or conditions under which units must stop or minimize their electromagnetic transmissions. EMCON is invoked when there is more danger from enemy intelligence detection of signals than the benefits those signals would provide. When EMCON is in effect, there still can be communications using mechanisms that do not radiate, including messengers, optical fiber networks, and line-of-sight laser or other low-probability-of-intercept technologies.
Operations defines the operational communications requirement, Intelligence defines the enemy exploitation threat, and Communications-Electronics works out the detailed Information Security (INFOSEC) and Communications Security (COMSEC) doctrine, in compliance with policies set by higher headquarters.
Divisions without standardized numbers
Force Development (U.S. JCS J-7)
While its designation will vary, a national, or at least service-level staff, often will have a division concerned with future force development, testing interoperability with other services and countries, and new doctrine development. In the U.S. Joint Staff, the Director for Operational Plans and Joint Force Development, works on enhancing joint force development through war plans, doctrine, education, training, exercises, and the assessment of each through the observation of Commanders in Chief and CJCS exercises and real world operations.
Through its four subordinate divisions, the J-7 acts as functional agent to support and facilitate the Chairman’s transformation efforts, and to pursue joint force development through joint doctrine;
- joint tactics, techniques and procedures;
- joint education;
- joint training;
- war plan assessments.
Budget (Eurocorps G-8)
Placed here is the preparation of the multinational communally funded Eurocorps (EC) budget, as well as audit of financial and contracting. It provides the Headquarters with the necessary financial, audit and contracting support. The Eurocorps organization must comply with NATO, EU, and national component rules. . 
Tactical and operational deception usually are in a compartmented cell of the Operations branch. Strategic deception is a national-level operation, as with the Allied London Controlling Staff and U.S. Joint Security Control 
Broader than the Western concept of strategic deception, however, is the Soviet and Russian doctrine of maskirovka, which was controlled at the highest levels of Red Army General Staff. The term translates poorly; "deception" and "camouflage" both convey some, but not all, of the significance.  Smith suggests it should be assumed to contain the English words, camouflage, concealment, deception, imitation, disinformation, secrecy, security, feints, diversions, and simulation, but go beyond them.
"Differing U.S. and Soviet perspectives on the principle of surprise, and the place that surprise holds within the respective doctrines, are key to much of the contrast between our deceptive practices and Soviet maskirovka."  Soviet writings emphasize historical experience, the changes in the nature of war since that experience, and the ways makirovka must change to be relevant to current conditions. Those changes must reflect the improvement in intelligence collection, the greater effect of weapons, and the increased tempo of operations. Taken together, these become a significant staff responsibility.
Civil and Military Operations (CMO)/Civil Affairs
Purely from a historical standpoint, Civil Affairs (sometimes Civil-Military Operation) seems to have difficulty fitting into a staff. For a time, the U.S. put into branch 5, but "5" tended, at higher headquarters level, to be "Plans and Policy", complementing the short-term planning in branch 3. To further confuse it, civil-military operations is part of information operations, which is apt to be in branch 3 as well.
In Eurocorps, civil-military operations are in G-9, and organized into three sections:
Especially in peace operations, a civil-military operations officer will usually be in the first staff group to arrive in the area of operations. As long as the situation is not a "hot war" response, G-9 needs to get in early, and establish and maintain relationship with the non-military actors in the AO:
- civilian authorities of the host nation
- the international and non-governmental organizations
- all other stakeholders acting in the area of operation including the most important one: the population
- the most delicate: opposition or insurgent forces.
Again part of information operations is public affairs, which also can be called "white propaganda", or official and acknowledged announcements. CMO strives to get a widely accepted understanding of the role of the military force. It may go beyond information into mediation and other forms of conflict resolution.
CMO can call on the force to assist in actions to assist the civilian population, subject to overriding tactical needs and budget/contracting guidance:
- Logistics: assets for refugees or displaced persons
- Engineer expertise on mines (de-mining, mine awareness) or request the execution of projects like repairing buildings, restoring electricity, water supply and so on.
- Medical: deal with public health problems
- Legal: help with interpretations of agreements, and, where appropriate, draft new ones where there are new stakeholders
- Military police: restoring civil order
- US Department of Defense (12 July 2007), Joint Publication 1-02 Department of Defense Dictionary of Military and Associated Terms
- Eurocorps, Engineer Branch
- U.S. V Corps, Staff Engineer Section
- Eurocorps, G2 Branch
- Martens, Ted L. (July, 2000), "The Brigade Combat Team—The Transformation Process", Military Intelligence Professional Bulletin
- Eurocorps, G3 Branch: Operations related matters are G3’s responsibility
- Sevalia, Roy C. & David C. Sims (16 December 1999), "Fighting Deep with Joint Fires", Air & Space Power Journal
- Pagonis, William G. (1992), Moving Mountains, Harvard Business Publishing
- Eurocorps, G4 Cite error: Invalid
<ref>tag; name "EurocorpsG8" defined multiple times with different content
- Eurocorps, G-5 Branch
- Joint Chiefs of Staff, J-7 Operational Plans and Joint Force Development
- Brown, Anthony Cave (1975), Bodyguard of Lies, HarperCollins
- Smith, Charles L. (Spring 1988), "Soviet Maskirovko", Airpower Journal
- Krueger, Daniel W. (04 December 1987), Maskirovka--What's in it for Us?, School of Advanced Military Studies, U.S. Army War College, ADA190836