United States Army
The army provides trained forces to the combatant commanders for use as directed by the secretary of defense.
By 2013, the army shifted to six geographical commands that align with the six geographical unified combatant commands (CCMD):

United States Army Central headquartered at Shaw Air Force Base, South Carolina
United States Army North headquartered at Fort Sam Houston, Texas
United States Army South headquartered at Fort Sam Houston, Texas
United States Army Europe and Africa headquartered at Clay Kaserne, Wiesbaden, Germany
United States Army Pacific headquartered at Fort Shafter, Hawaii
The army also transformed its base unit from divisions to brigades. Division lineage will be retained, but the divisional headquarters will be able to command any brigade, not just brigades that carry their divisional lineage. The central part of this plan is that each brigade will be modular, i.e., all brigades of the same type will be exactly the same and thus any brigade can be commanded by any division. As specified before the 2013 end-strength re-definitions, the three major types of brigade combat teams are:

Armored brigades, with a strength of 4,743 troops as of 2014.
Stryker brigades, with a strength of 4,500 troops as of 2014.
Infantry brigades, with a strength of 4,413 troops as of 2014.
In addition, there are combat support and service support modular brigades. Combat support brigades include aviation (CAB) brigades, which will come in heavy and light varieties, fires (artillery) brigades (now transforms to division artillery) and expeditionary military intelligence brigades. Combat service support brigades include sustainment brigades and come in several varieties and serve the standard support role in an army.

Combat maneuver organizations: To track the effects of the 2018 budget cuts, see Transformation of the United States Army#Divisions and brigades
The U.S. Army's conventional combat capability currently consists of 11 active divisions and 1 deployable division headquarters (7th Infantry Division) as well as several independent maneuver units.
From 2013 through 2017, the Army sustained organizational and end-strength reductions after several years of growth. In June 2013, the Army announced plans to downsize to 32 active brigade combat teams by 2015 to match a reduction in active-duty strength to 490,000 soldiers. Army chief of staff Raymond Odierno projected that the Army was to shrink to "450,000 in the active component, 335,000 in the National Guard and 195,000 in U.S. Army Reserve" by 2018. However, this plan was scrapped by the incoming Trump administration, with subsequent plans to expand the Army by 16,000 soldiers to a total of 476,000 by October 2017. The National Guard and the Army Reserve will see a smaller expansion.
The Army's maneuver organization was most recently altered by the reorganization of United States Army Alaska into the 11th Airborne Division, transferring the 1st and 4th Brigade Combat Teams of the 25th Infantry Division under a separate operational headquarters to reflect the brigades' distinct, Arctic-oriented mission. As part of the reorganization, the 1–11 (formerly 1–25) Stryker Brigade Combat Team will reorganize as an Infantry Brigade Combat Team. Following this transition, the active component BCTs will number 11 Armored brigades, 6 Stryker brigades, and 14 Infantry brigades.
Within the Army National Guard and United States Army Reserve, there are a further eight divisions, 27 brigade combat teams, additional combat support and combat service support brigades, and independent cavalry, infantry, artillery, aviation, engineer and support battalions. The Army Reserve in particular provides virtually all psychological operations and civil affairs units.
 United States Army Forces Command (FORSCOM)

For a description of U.S. Army tactical organizational structure, see: a U.S. context and also a global context.

Special operations forces: United States Army Special Operations Command (Airborne) (USASOC):

Medical Department: The United States Army Medical Department (AMEDD), formerly the Army Medical Service (AMS), is the primary healthcare organization of the United States Army and is led by the Surgeon General of the United States Army (TSG), a three-star lieutenant general, who (by policy) also serves as the Commanding General, United States Army Medical Command (MEDCOM). TSG is assisted by a Deputy Surgeon General and a full staff, the Office of the Surgeon General (OTSG). The incumbent Surgeon General is Lieutenant General Mary K. Izaguirre (since January 25, 2024).
AMEDD encompasses the Army's six non-combat, medical-focused specialty branches (or "Corps"), these branches are: the Medical Corps, Nurse Corps, Dental Corps, Veterinary Corps, Medical Specialist Corps. Each of these branches is headed by a Corps Chief that reports directly to the Surgeon General.

Personnel: The Army's Talent Management Task Force (TMTF) has deployed IPPS-A, the Integrated Personnel and Pay System - Army, an app which serves the National Guard, and on 17 January 2023 the Army Reserve and Active Army. Soldiers were reminded to update their information using the legacy systems to keep their payroll and personnel information current by December 2021. IPPS-A is the Human Resources system for the Army, is now available for download for Android, or the Apple store. It will be used for future promotions and other personnel decisions. Among the changes are:

BCAP, the Battalion Commander Assessment Program. In January 2020, over 800 majors and lieutenant colonels from all over the Army converged on Fort Knox to take part in a five-day program to select the next battalion commanders for the Army (beginning in FY2021). This process replaces the former selection process which was based solely on rank and individual reviews of past performance. From now on, more consideration will be given to an individual officer's personal preference, as part of 25 other selection criteria. "Promotion boards will now be able to see almost all substantiated adverse information". The promotion boards will be able to see anything in an officer's human resource record. Officers are encouraged to become familiar with their human resource record, and to file rebuttals to adverse information.
Depending on the success of this initiative, other assessment programs could be instituted as well, for promotion to sergeants major, and for assessment of colonels for command.
Below are the U.S. Army ranks authorized for use today and their equivalent NATO designations. Although no living officer currently holds the rank of General of the Army, it is still authorized by Congress for use in wartime.

Officers: There are several paths to becoming a commissioned officer including the United States Military Academy, Reserve Officers' Training Corps, Officer Candidate School, and direct commissioning. Regardless of which road an officer takes, the insignia are the same. Certain professions including physicians, pharmacists, nurses, lawyers and chaplains are commissioned directly into the Army.
Most army commissioned officers (those who are generalists) are promoted based on an "up or out" system. A more flexible talent management process is underway. The Defense Officer Personnel Management Act of 1980 establishes rules for the timing of promotions and limits the number of officers that can serve at any given time.
Army regulations call for addressing all personnel with the rank of general as "General (last name)" regardless of the number of stars. Likewise, both colonels and lieutenant colonels are addressed as "Colonel (last name)" and first and second lieutenants as "Lieutenant (last name)".

Warrant officers: Warrant officers are single track, specialty officers with subject matter expertise in a particular area. They are initially appointed as warrant officers (in the rank of WO1) by the secretary of the Army, but receive their commission upon promotion to chief warrant officer two (CW2).
By regulation, warrant officers are addressed as "Mr. (last name)" or "Ms. (last name)" by senior officers and as "sir" or "ma'am" by all enlisted personnel. However, many personnel address warrant officers as "Chief (last name)" within their units regardless of rank.

Enlisted personnel: Sergeants and corporals are referred to as NCOs, short for non-commissioned officers. This distinguishes corporals from the more numerous specialists who have the same pay grade but do not exercise leadership responsibilities. Beginning in 2021, all corporals will be required to conduct structured self-development for the NCO ranks, completing the basic leader course (BLC), or else be laterally assigned as specialists. Specialists who have completed BLC and who have been recommended for promotion will be permitted to wear corporal rank before their recommended promotion as NCOs.
Privates and privates first class (E3) are addressed as "Private (last name)", specialists as "Specialist (last name)", corporals as "Corporal (last name)" and sergeants, staff sergeants, sergeants first class and master sergeants all as "Sergeant (last name)". First sergeants are addressed as "First Sergeant (last name)" and sergeants major and command sergeants major are addressed as "Sergeant Major (last name)".

Training: Training in the U.S. Army is generally divided into two categories – individual and collective.