A master sergeant is the military rank for a senior non-commissioned officer in the armed forces of some countries.

The רב-סמל ראשון‎ rav samal rishon (abbreviated "rasar", master sergeant) is a non-commissioned officer (נגדים‎) rank in the Israel Defense Forces (IDF).

The ranks are derived from those of the paramilitary Haganah developed in the British Mandate of Palestine period to protect the Yishuv.

[1] Master sergeant is used by the Armed Forces of the Philippines as a non-commissioned officer rank.

A master sergeant may be assigned as a brigade-level section noncommissioned officer in charge and serves as the subject matter expert in their field, but may also hold other positions depending on the type of unit.

Use of the term "top" or "master sergeant" is not a requirement, but is considered courteous, and remains to be at the discretion of the one addressing the master sergeant, though "top" is preferred, due to the long tradition of its use in the U.S. Army, which has, since the Civil War, emphasized the importance of senior NCOs closely advising and instructing newly commissioned second lieutenants, first lieutenants and captains.

In the U.S. Marine Corps, master sergeants provide technical leadership as occupational specialists at the E-8 level.

Infantry master sergeants also serve as the assistant operations chief in the S-3 section of the headquarters of an infantry regiment and Marine Expeditionary Unit and in the G-3 section of the headquarters of a Marine Expeditionary Brigade.

Only in the Marine Corps are master sergeants required to be addressed by their full rank.

At the rank of master sergeant, the airman enters the senior non-commissioned tier and transitions his or her duties from front line technicians and supervisors to operational leaders.

In 1991, the Air Force changed its NCO insignia so that a maximum of five stripes, or rockers, were placed on the bottom of the chevrons.

The master sergeant rank insignia was changed by removing the bottom (sixth) rocker, and relocating it above as a single chevron, on top of the five lower stripes.

In 2015, the Air Force announced its promotion overhaul and newly established boards for master sergeant.