The military services have never established clear and consistent service-wide definitions for the categories of the medals they award. As a result, the boundaries between them are often fuzzy and confusing. The reason is simple: United States military medals have developed over a period of more than 145 years, most of them over the last half-century. Nearly all of them were created to meet what was perceived as a specific need at the time. Since the individual military services have always looked at things from the perspective of their own culture, they have rarely analyzed the collective impact of all the medals that have been created. Moreover, neither the individual Military Services nor the Department of Defense has developed a cross-service decision logic (or "first principles") to be applied when considering the establishment of new or future medals.

Another fundamental problem is that the Military Services have never even agreed upon "first principles" for designing medals, for the use of color schemes in their ribbons, or for the devices or attachments they place on them. Finally, there is no clear consensus on who can or should authorize medals. Some have been created by Congress; others have been created by the President, and yet others have been established by either the Service Secretaries or even the Service Chiefs.

In spite of this chaos, general patterns have emerged over time. Campaign and expeditionary medals have historically been used to recognize participation in military operations against an armed and hostile enemy. Service medals, on the other hand, recognize either noteworthy non-combat military service or military service under noteworthy conditions. In most instances, that service does not involve direct participation in combat operations. Service medals fall into the five broad categories shown at the top of this page. For information on the medals within these specific categories, click on the category.