The Meritorious Service Medal (MSM) is a military award presented to members of the United States Armed Forces who distinguished themselves by outstanding meritorious achievement or service to the United States subsequent to January 16, 1969.

The MSM was previously awarded as a decoration for achievement during peacetime, but effective September 11, 2001 this decoration may also be bestowed in lieu of the Bronze Star Medal for meritorious achievement in a designated combat theater. Normally, the acts or services rendered must be comparable to that required for the Legion of Merit but in a duty of lesser, though considerable, responsibility. Within the U.S. Army, according to AR 600-8-22, Paragraph 3-16, the MSM may not be upgraded to or downgraded from a recommended Bronze Star Medal. In the Army, an MSM recommendation that is downgraded will be approved as an Army Commendation Medal (ARCOM).

A higher award and decoration, the Defense Meritorious Service Medal (DMSM), is intended for similar services performed under joint duty within the United States Department of Defense, to include the Joint Staff, the Unified Combatant Commands, and joint task forces under their cognizance.

The Meritorious Service Medal (MSM) is given to all ranks for meritorious service in the Army, Air Force, and Space Force. Award of the MSM may be for meritorious performance while serving in a staff position as a field grade officer, senior chief warrant officer, or senior non-commissioned officer, or, in the case of field grade officers, for successful completion of a command tour at the battalion (Army) or squadron (Army, Air Force, or Space Force) level. Award of the MSM to company grade officers in pay grades O-1 through O-3 (second lieutenant, first lieutenant, captain), junior warrant officers and chief warrant officers in pay grades W-1 and W-2 (WO1 and CW2, Army only), and junior NCOs in pay grades E-6 and below is rare and typically by exception.

The U.S. Navy, U.S. Marine Corps, and U.S. Coast Guard subscribe to a slightly different philosophy from the Army, Air Force, and Space Force in awarding the MSM, typically reserving it for senior Navy and Coast Guard officers in pay grades O-5 to O-6 (commander and captain) and Marine Corps field grade officers in pay grades O-5 and O-6 (lieutenant colonel and colonel), with the first award of the MSM typically occurring after completion of a successful commanding officer assignment at the O-5 level. Award of the MSM to USN, USMC, and USCG officers in pay grade O-4 (USN & USCG lieutenant commander / USMC major) and below, to include chief warrant officers and below (other than as an award at retirement to CWO5 and CWO4) is typically by exception and normally limited to those who have held one of the service's handful of O-4–level commanding officer assignments (e.g., Avenger-class mine countermeasures ship) or serving on a USN or USCG flag officer staff or USMC general officer staff.

Enlisted award of the MSM in the Navy, Marine Corps, and Coast Guard is likewise typically limited to pay grades E-8 (e.g., USN/USCG senior chief petty officer and USMC master sergeant or first sergeant) and E-9 (e.g., USN/USCG master chief petty officer and USMC sergeant major or master gunnery sergeant), while award of the MSM to pay grade E-7 (e.g., USN/USCG chief petty officer and USMC gunnery sergeant) and below is very rare and by exception. In the Navy, Marine Corps, and Coast Guard, the awarding authority for the MSM must be either a flag officer or general officer holding the pay grade of O-7 or above. It is most common for Navy and Coast Guard master chief petty officers (typically command master chief petty officers) and Marine Corps master gunnery sergeants and sergeants major to receive the MSM as an end-of-tour award or upon retirement.

Foreign military personnel in the ranks of NATO OF-5 (US O-6 equivalent) and below and individuals who have displayed a level of service that warrants an award of such magnitude may also be eligible to be awarded the MSM, subject to approval by a U.S. flag officer or general officer. To receive this medal, the individual must exhibit exceptionally meritorious service at that level of responsibility.