Malaysia Airlines Flight 370 (MH370/MAS370) was a scheduled international passenger flight operated by Malaysia Airlines that disappeared on 8 March 2014 while flying from Kuala Lumpur International Airport in Malaysia to its planned destination, Beijing Capital International Airport. The crew of the Boeing 777-200ER registered as 9M-MRO, last communicated with air traffic control (ATC) around 38 minutes after takeoff when the flight was over the South China Sea. The aircraft was lost from ATC radar screens minutes later, but was tracked by military radar for another hour, deviating westwards from its planned flight path, crossing the Malay Peninsula and Andaman Sea. It left radar range 200 nautical miles (370 km) northwest of Penang Island in northwestern Peninsular Malaysia.

With all 227 passengers and 12 crew aboard presumed dead, the disappearance of Flight 370 was the deadliest incident involving a Boeing 777 and the deadliest in Malaysia Airlines' history until it was surpassed in both regards by Malaysia Airlines Flight 17, which was shot down while flying over conflict-stricken Eastern Ukraine four months later. The combined loss caused significant financial problems for Malaysia Airlines, which was renationalised by the Malaysian government in August 2014.

The search for the missing airplane, which became the most expensive in aviation history, focused initially on the South China Sea and Andaman Sea, before analysis of the aircraft's automated communications with an inmarsat satellite indicated a possible crash site somewhere in the southern Indian Ocean. The lack of official information in the days immediately after the disappearance prompted fierce criticism from the Chinese public, particularly from relatives of the passengers, as most people on board Flight 370 were of Chinese origin. Several pieces of marine debris confirmed to be from the aircraft washed ashore in the western Indian Ocean during 2015 and 2016. After a three-year search across 120,000 km2 (46,000 sq mi) of ocean failed to locate the aircraft, the Joint Agency Coordination Centre heading the operation suspended its activities in January 2017. A second search launched in January 2018 by private contractor Ocean Infinity also ended without success after six months.

Relying mostly on analysis of data from the Inmarsat satellite with which the aircraft last communicated, the Australian Transport Safety Bureau (ATSB) proposed initially that a hypoxia event was the most likely cause given the available evidence, although no consensus has been reached concerning this theory among investigators. At various stages of the investigation, possible hijacking scenarios were considered, including crew involvement, and suspicion of the airplane's cargo manifest; many disappearance theories regarding the flight have also been reported by the media. The Malaysian Ministry of Transport's final report from July 2018 was inconclusive, but highlighted Malaysian ATC's failures to attempt to communicate with the aircraft shortly after its disappearance. In the absence of a definitive cause of disappearance, air transport industry safety recommendations and regulations citing Flight 370 have been intended mostly to prevent a repetition of the circumstances associated with the loss. These include increased battery life on underwater locator beacons, lengthening of recording times on flight data recorders and cockpit voice recorders, and new standards for aircraft position reporting over the open ocean.