A United States defense standard, often called a military standard, "MIL-STD", "MIL-SPEC", or (informally) "MilSpecs", is used to help achieve standardization objectives by the United States Department of Defense.

Standardization is beneficial in achieving interoperability, ensuring products meet certain requirements, commonality, reliability, total cost of ownership, compatibility with logistics systems, and similar defense-related objectives.

Defense standards are also used by other non-defense government organizations, technical organizations, and industry. This article discusses definitions, history, and usage of defense standards. Related documents, such as defense handbooks and defense specifications, are also addressed.

Although the official definitions differentiate between several types of documents, all of these documents go by the general rubric of "military standard", including defense specifications, handbooks, and standards. Strictly speaking, these documents serve different purposes. According to the Government Accountability Office (GAO), military specifications "describe the physical and/or operational characteristics of a product", while military standards "detail the processes and materials to be used to make the product." Military handbooks, on the other hand, are primarily sources of compiled information and/or guidance. The GAO acknowledges, however, that the terms are often used interchangeably.

Official definitions are provided by DoD 4120.24, Defense Standardization Program (DSP) Procedures, November 2014, USD (Acquisition, Technology and Logistics):

For purposes of this article, "military standards" will include standards, specifications and handbooks.

There are also standard names with different letters behind ′MIL-′ like MIL-C-5040H, MIL-E-7016F or MIL-S-901.

The DOD has standards about the format of standards: