The Alaska State Defense Force (ASDF) is the state defense force of Alaska. It is one of 18 such forces in the United States. The Alaska State Defense Force is administered under the Alaska Department of Military and Veterans Affairs, but is headed by a commander who reports directly to the governor of Alaska, who acts as commander-in-chief of the state defense force.

The Alaska State Defense Force is the successor of the Alaska Territorial Guard founded during World War II. With the conclusion of the war and Alaska's inauguration as a state in 1959, the Territorial Guard was disbanded but soon replaced by a state militia established by state statute. In 1984, the Alaska State Guard was formed; it was renamed in 1987 as the Alaska State Defense Force. In 2004, the name 49th Military Police Brigade (49th MP BDE) was also adopted for it. A later realignment of the command's structure has utilized the new designation of 49th Readiness Brigade (Separate), but the unit is still mainly known as the Alaska State Defense Force.

The ASDF structure was primarily composed of military police units. The units operated with mostly state certified constables under the Alaska Police Standards Council. By statute, the Alaska State Defense Force must be made up of no less than 75 percent former military personnel.

Following the September 11 attacks, the ASDF was tasked with guarding critical oil infrastructure against attack.

Unlike most of the state defense forces in the United States, Alaska State Guardsmen trained and certified with firearms in order to achieve proficiency to carry firearms when activated. However, in 2008, following an investigation of the leadership of Brigadier General Thomas Westall, then serving as the head of the ASDF, Governor Sarah Palin ordered the ASDF to disarm. The current structure of the ASDF is as a Readiness Brigade composed of readiness battalions. The military police (MP) function is in abeyance until needed by the Adjutant General for Alaska.

In 2016, Governor Bill Walker announced his intention to reform the Alaska State Defense Force by expanding it further into rural Alaska, bringing the level of training closer to that of the National Guard, and creating a signal detachment. On 14 January 2016, the Alaska State Defense Force activated the 2nd Signal Detachment, a component of the 49th Brigade. On 15 September, 2017, the Alaska State Defense Force activated a Scout Detachment in the Native Village of Kwethluk. In 2017, Alaska State Defense Force members, in their first ever deployment outside of the state, provided support to relief efforts in Puerto Rico alongside Alaska National Guardsmen after Hurricane Maria and Irma caused extensive damage to the island. State and National Guardsmen provided communications support at a Joint Incident Site Communications Capability system.

In March 2018, the Alaska State Defense Force took part in an international training exercise, working directly with their Canadian counterparts, the Canadian Rangers, in a combined domain awareness capacity drill.

In April 2020, members of the Alaska State Defense Force were activated to assist in Alaska's response to the COVID-19 pandemic. Members worked at an Anchorage warehouse to help organize personal protective equipment and other supplies from the national stockpile and putting them into loads for shipment. Members also helped distribute declaration forms for people entering the state who must quarantine themselves.