There are four paths to optaining a commission within the United States military, each has specific requirements and elements that are often indicative of the career or specialty of which the officer aspires.  All commissioned officers must be college graduates, and a relatively few of them are commissioned from enlisted soldiers (these officers who were once enlisted are typically called "mustangs" and are more common in time of war).

The Reserve Officers Training Corps (ROTC):  The largest percentage of officers in todays military are graduates ofthe Reserve Officers Training Corps, which operates at thousands of colleges across the country.  Cadets attend regular civilian universities and take military training courses over the course of their studies, receiving a commission at graduation.  Some but not all ROTC cadets go to college on scholarships payed for by the military and requiring a specific term of military service upon completion.  These typically come in 2, 3, and 4-year programs.  The marine corps recieves officers through the Naval ROTC program.

Officers Candidate School (OCS):  A 14-16 week course depending on the service, OCS students go through an extended basic training.  OCS is often the route chosen by those who already have a college degree, or who aspire to certain specialties such as pilot training which may be combined with the OCS program.

The Service Academies:  The most prestigeious and once the primary means of creating officers, the service academies (West Point, Annapolis, and the Air Force Academy) still graduate a high presentage of officers destined for the higher ranks.  Many ROTC and OCS officers consider the Academies to be old fashioned institutions with an inflated opinion of their own importance to their parent services.  Graduates are often called "ring knockers" because they are said to knock their graduation rings togeather while shaking hands on their way up through the old boys network of the services.  The first class of women at all three institutions was the class of 1980 (entering in 1976 following the passage of a law by congress forcing the issue).  Many of the women from the classes graduating in the 1980s tell horror stories of abuse and degredation.

Students spend their summers training on actual military bases and persuing specialized training.  Originally founded as, and still primarily engineering schools, if a cadet or midshipmen fails out of the academy after his or her second year, he must pay back the government for the coast of his education.  Graduates are required to serve four years as an active duty officer.

There are a number of private or state funded military academies across the country, most prominent of them the Virginia Military Institute, the Citedal (in South Carolina), and Norwich (in Vermont).  These graduate officers through the ROTC program and are not considered part of the service academy system.

The United States Military Academy (USMA):  Known as West Point, the academy was founded as the country's first engineering school on the site of stretegic battlements form the Revolutionary War.  Along the Hudson River in upstate New York, the vast majority of its graduates go into the army, though occasionally a West Point graduate will seek a commission in one of the other services.  A number of U.S. Presidents have graduated from West Point, the last of which was Dwight Eisenhower.

The United States Naval Academy (USNA):  Known as Annapolis, after the Maryland city where the school is based, the Naval Academy also provides officers for the United States Marine Corps as well as the Navy.  In recent years it has been racked by cheating scandals.  Unlike the other two academies, students at Annapolis are called Midshipmen, and usually referred to as Mr. or Miss.

The United States Air Force Academy (USAFA):  The youngest of the academies, the Air Force Academy is situated in Colorado Springs and is not primarily oriented to graduating pilots.  In recent years the academy has been the subject of accusations that it ignored the rape of female cadets.  In Stargate: SG1 Major Samantha Carter is a graduate of the Air Force Acadmey and scenes in several episodes are set there.

Other schools within the military structure include the Army War College, the Naval War College, and the Uniformed University of the Health Sciences, all of which offer advanced degrees for those who are already commissioned officers.

Direct Commissions:  Officers with extremely specialized skills, such as chaplains, and scientists are often given direct commissions withing the services.  These rarely come with military training beyond how to salute, march, and wear a uniform, and the offices directly commissioned are never placed in the chain of command.  Though doctors and lawyers are often commissioned this way, others chose to go through OCS to improve their career possibilities.