Fort Indiantown Gap, also referred to as "The Gap" or "FIG",^{[citation needed]} is a census-designated place and National Guard Training Center primarily located in East Hanover and Union townships in Lebanon County, Pennsylvania, United States. (A portion of the installation is located in eastern Dauphin County.) It is located adjacent to Interstate 81, 23 miles (37 km) northeast of Harrisburg, just north of the northern terminus of Pennsylvania Route 934 at I-81's Exit 85.

The installation is an active National Guard Training Center and serves as headquarters for the Pennsylvania Department of Military and Veterans Affairs and the Pennsylvania National Guard. The post includes about 18,000 acres (73 km²) of land, with numerous ranges and training areas for the Pennsylvania National Guard and other active-duty and reserve-component military units as well as law-enforcement agencies. The reservation is protected by the Fort Indiantown Gap Police Department, a full-time department which also enforces traffic and other state laws. The force is an agency of the Department of Military and Veterans Affairs.

The installation surrounds Memorial Lake State Park and Indiantown Gap National Cemetery. It is served by the Annville, Pennsylvania post office, ZIP Code 17003. As of the 2010 census the population was 143 residents. State House, the former official residence of the Lieutenant Governor of Pennsylvania, is located on the grounds.

The history of Fort Indiantown Gap dates to 1755, when the colonial government established several forts as defenses for White settlers against the Susquehannock. Tensions had risen as the colonists encroached on the communal lands of the Susquehannock, who had long hunted and cultivated there. The Native Americans became willing allies against the British colonists as the French and Indian War began. At the onset of the war, the Susquehannock attacked colonial frontier settlements, using the passes that existed in Blue Mountain through Manada Gap, Indiantown Gap, and Swatara Gap. Because of these attacks, fortifications were established near Swatara Gap in northern Lebanon County, just east of present-day Fort Indiantown Gap, and near Manada Gap in Dauphin County.

The name Indiantown Gap was fashioned from the Native American presence and geography. “Indiantown” is derived from the many Native American villages that existed in the vicinity of the installation, and “Gap” refers to the separation in the Blue Mountains through which the creek known as Indiantown Run flows.

The current post was originally developed by the Commonwealth of Pennsylvania, on the recommendation of General Edward Martin, as a National Guard training site in 1931 after the Pennsylvania National Guard outgrew its 120-acre training site at Mount Gretna, Pennsylvania.

Over the years, the installation has served as home to the Pennsylvania National Guard as well as active units of the United States Army. In 1941, the post was officially named Indiantown Gap Military Reservation (IGMR). Martin retired from military service and later served as governor of Pennsylvania and then as a U.S. senator for Pennsylvania. After his death, the Pennsylvania General Assembly renamed the installation the Edward Martin Military Reservation, a designation that Martin himself had rejected throughout his life. The new name was never fully accepted by the military personnel who served there.

In 1975, the Secretary of the Army renamed the post Fort Indiantown Gap, in order to more closely align it with other Active Duty stations throughout the United States. Pennsylvania also reinstated the Indiantown Gap designation, which it retains today.