The Defense Meritorious Service Medal (DMSM) is the third-highest award bestowed upon members of the United States military by the United States Department of Defense. The medal is awarded in the name of the Secretary of Defense to members of the Armed Forces who, while serving in a joint activity, distinguish themselves by non-combat outstanding achievement or meritorious service, but not of a degree to warrant award of the Defense Superior Service Medal.

The medal was first created in 1977 and was first awarded to Major Terrell G. Covington, United States Army.

Additional awards of the Defense Meritorious Service Medal are denoted by oak leaf clusters. The medal is not the same as the Meritorious Service Medal, which is a separate federal military decoration. Both have virtually identical award criteria, but the DMSM is awarded to servicemembers assigned to joint, multi-service organizations, while the MSM is awarded to servicemembers in traditional military units.