The Northrop Grumman B-2 Spirit (also known as the Stealth Bomber) is an American heavy bomber with "low observable" stealth technology designed to penetrate dense anti-aircraft defenses and deploy both conventional and nuclear weapons. Because of its considerable capital and operations costs, the project was controversial in Congress and among Pentagon brass. During the late 1980s and early 1990s, Congress slashed initial plans to purchase 132 bombers to just 21.

The cost of each aircraft averaged US$737 million in 1997 dollars. Total procurement costs averaged US$929 million per aircraft, which includes spare parts, equipment, retrofitting, and software support. The total program cost, which includes development, engineering and testing, averaged US$2.1 billion per aircraft (in 1997 dollars).

Twenty B-2s are operated by the United States Air Force. Though originally designed in the 1980s for Cold War operations scenarios, B-2s have been used in combat to drop bombs on Serbia during the Kosovo - Serbia Conflict in the late 1990s, and saw continued use during the ongoing wars in Iraq and Afghanistan. One aircraft was lost when it crashed on takeoff in 2008.

The bomber has a crew of two and can drop up to 80 x 500 lb (230 kg)-class JDAM GPS-guided bombs, or 16 x 2,400 lb (1,100 kg) B83 nuclear bombs in a single pass through extremely dense anti-aircraft defenses. The B-2 is the only aircraft that can carry large air to surface standoff weapons in a stealth configuration. The program has been the subject of espionage and counter-espionage activity and the B-2 has been prominent public spectacles at air shows since the 1990s.

The B-2 Spirit originated from the Advanced Technology Bomber (ATB) black project that began in 1979. The Cold War was well underway, and on the campaign trail in 1979 and 1980, candidate Ronald Reagan promised a restoration of American military strength. On 22 August 1980, the incumbent Carter administration publicly disclosed that the Department of Defense was working to develop stealth aircraft including the ATB. In 2007, it was revealed publicly that MIT scientists helped assess the mission effectiveness of the aircraft under classified contract during the 1980s.

After the evaluations of the companies' proposals, the ATB competition was reduced to the Northrop/Boeing and Lockheed/Rockwell teams with each receiving a study contract for further work. The Northrop design was larger while the Lockheed design was smaller and included a small tail. The black project was funded under the code name "Aurora". The Northrop/Boeing team's ATB design was selected over the Lockheed/Rockwell design on 20 October 1981.

The Northrop design received the designation B-2 and the name "Spirit". The bomber's design was changed in the mid-1980s when the mission profile was changed from high-altitude to low-altitude, terrain-following. The redesign delayed the B-2's first flight by two years and added about US$1 billion to the program's cost. An estimated US$23 billion was secretly spent for research and development on the B-2 by 1989. At the program's peak, approximately 13,000 people were employed at a dedicated plant in Pico Rivera, California for the aircraft's engineering and portions of its manufacturing.

The B-2 was first publicly displayed on 22 November 1988, at Air Force Plant 42, Palmdale, California, where it was assembled. Its first public flight was on 17 July 1989 from Palmdale.