APL has developed numerous systems and technologies in the areas of air and missile defense, surface and undersea naval warfare, computer security, and space science and spacecraft construction.

[4] While APL provides research and engineering services to the government, it is not a traditional defense contractor, as it is a UARC and a division of Johns Hopkins University.

[5] APL was created in 1942 during World War II under the Office of Scientific Research and Development's Section T[6] as part of the Government's effort to mobilize the nation's science and engineering expertise within its universities.

[9] Section T's Applied Physics Laboratory succeeded in developing the variable-time proximity fuze[10] that played a significant role in the Allied victory.

[12] Expected to disband at the end of the war, APL instead became heavily involved in the development of guided missile technology for the Navy.

The Laboratory's name comes from its origins in World War II, but APL's major strengths are systems engineering and technology application.

APL conducts programs in fundamental and applied research; exploratory and advanced development; test and evaluation; and systems engineering and integration.

[3] The building also includes a four-story atrium, a STEM Center and a combination of 100 huddle, conference and auditorium breakout rooms.

[26][27] As of APL's 80th anniversary in 2022, there were hundreds of projects spanning the Lab's 12 mission areas, that focus on solving complex research, engineering and analytical problems that present critical challenges to the United States.

In 2014, APL made history with the successful use of the Modular Prosthetic Limb — a fully artificial articulated arm and hand — by a bilateral shoulder-level amputee.

APL used pattern recognition algorithms to track which muscles were contracting and enable the prosthetics to move in conjunction with the amputee's body.

[34] Similar technology was used in 2016 for a demonstration in which a paralyzed man was able to "fist-bump" Barack Obama using signals sent from an implanted brain chip.

In 2023, APL announced that researchers have developed one of the world's smallest, most intense and fastest refrigeration devices, the wearable thin-film thermoelectric cooler (TFTEC), and teamed with neuroscientists to help amputees perceive a sense of temperature with their phantom limbs.