This historical monograph is the first in a series of reserve regimental histories. A Brief History of the 25th Marines is a concise narrative of the regiment from its initial activation in 1943 through its participation in the battles for Roi-Namur, Saipan, Tinian and Iwo Jima during World War II, to its reactivation in the 1960s as a regiment in the Marine Corps Reserves, and subsequent training and civic activities. Official records of the Marine Corps and appropriate historical works were utilized in compiling this short history. This booklet is published for the information of those interested in the 25th Marines and in the events in which it took part.