The Pennsylvania National Guard is one of the oldest and largest National Guards in the United States Department of Defense. It traces its roots to 1747 when Benjamin Franklin established the Associators in Philadelphia.

With more than 18,000 personnel, the Pennsylvania National Guard is the second-largest of all of the state National Guards. It has the second-largest Army National Guard and the fourth-largest Air National Guard. These forces are respective components of the United States Army and Air Force.

The Pennsylvania National Guard is also part of the Pennsylvania Department of Military and Veterans Affairs, which is headed by Pennsylvania Adjutant General Brigadier General John Pippy. It is headquartered at Fort Indiantown Gap in Lebanon County, Pennsylvania and has facilities in more than eighty locations across the state.

The Pennsylvania National Guard dates back to 1747 when Ben Franklin created the Associators in Philadelphia. Having overcome the long pacifist tradition of Pennsylvania's founding Quakers, Benjamin Franklin lead approximately 600 "gentlemen and merchants" of Philadelphia in signing the Articles of Association to provide for a common defense against Indian raiders and French privateers. These "Associators" (today's 111th Infantry Regiment and 103rd Brigade Engineer Battalion) are recognized as the foundation of the Pennsylvania National Guard. Within months, the Philadelphia Associators had brother units throughout the commonwealth. In 1755, the Pennsylvania Assembly passed the first Militia Act, formally authorizing a volunteer militia.

Shortly after the start of the American Revolutionary War, the First Troop, Philadelphia City Cavalry escorted General George Washington to New York to take command of the Continental Army after it was created by an act of the Second Continental Congress on June 14, 1775. The Army's first units included a regiment of rifle companies from Pennsylvania. During the American Revolution, Pennsylvania supplied 6,000 troops—4,500 of them Associators—for military operations in New York. In all, tens of thousands of Pennsylvania soldiers were called to service over the next seven years.

After the American Revolution, the nation was put to the test when the militia in the Commonwealth of Pennsylvania was called upon to put down fellow citizens in the western part of the state during the Whiskey Rebellion. More than 4,000 militiamen from Pennsylvania served.

During the War of 1812, Pennsylvania forces again volunteered to defend the nation and the Commonwealth. Altogether, more than 14,000 Pennsylvanians actively served. During the Battle of Lake Erie, an artillery company provided volunteers to serve as cannoneers on Commodore Perry's fleet. That unit is known today as Wilkes-Barre's 109th Field Artillery Regiment. Future president James Buchanan was a private in the Pennsylvania militia during the defense of Baltimore.

During the Mexican War, Pennsylvania provided two regiments of volunteer militiamen from across the Commonwealth. Many of these companies that answered the call were already formed from existing regiments within Pennsylvania's militia structure.