The 1st Battalion 9th Marines (1/9) was an infantry battalion of the United States Marine Corps. Formed during World War I, it served until the mid-2000s when it was deactivated to make room for one of three light armor reconnaissance battalions. During the Vietnam War, 1/9 sustained the highest casualty rate in Marine Corps history. This earned them the nickname "The Walking Dead".

In late 2005, the battalion was reactivated and attached to the 8th Marine Regiment at MCB Camp Lejeune. Although the first full company has deployed, 1/9 was not expected to be ready for deployment as a battalion until May 2008. On 19 April 2007, 1/9 was officially stood up with all of its subordinate units fully manned.

As of 29 August 2014 the battalion has been deactivated due to a force shaping initiative and downsizing of the Marine Corps. On the occasion of this deactivation, one of its former officers lauded: "Not a better battalion in the world"