The Picatinny Arsenal (/ˈpɪkətɪni/ or /ˌpɪkəˈtɪni/) is an American military research and manufacturing facility located on 6,400 acres (26 km2) of land in Jefferson Township and Rockaway Township in Morris County, New Jersey, United States, encompassing Picatinny Lake and Lake Denmark. The Arsenal is the headquarters of the United States Army Armament Research, Development and Engineering Center. It is known for developing the ubiquitous Picatinny rail, as well as being the army's center of expertise for small arms cartridge ammunition.

The facility was founded in 1880 as the Picatinny Powder Depot. Soon afterward, the navy acquired a portion of the arsenal to establish the Lake Denmark Powder Depot, later known as Lake Denmark Naval Ammunition Depot. It manufactured gunpowder until after World War I, at which time the facility also began producing heavy munitions and grew more involved in research and development activities. During World War II Picatinny was a major large-caliber-round loading plant with 18,000 employees. Today, the facility develops new technologies for the US Armed Forces and builds various munitions, weapons and armor systems.

Picatinny Arsenal is also home to the US Army Explosive Ordnance Disposal Technology Directorate. This group is responsible for the creation of tools, equipment, and procedures for US Army EOD personnel. Some of their more recent inventions was the use of weapons on a robot platform and the SWORDS robot. Their building has been recently renamed in honor of one of their deceased soldiers, SFC Scott "Smitty" Smith, who was killed in Iraq in July 2006.