In 2006, Boeing started considering the replacement of the 737 with a "clean-sheet" design that could follow the Boeing 787 Dreamliner. In June 2010, a decision on this replacement was postponed into 2011.
On December 1, 2010, Boeing's competitor, Airbus, launched the Airbus A320neo family to improve fuel burn and operating efficiency with new engines: the CFM International LEAP and Pratt & Whitney PW1000G. In February 2011, Boeing's CEO Jim McNerney maintained "We're going to do a new airplane." At the March 2011 ISTAT conference, BCA President James Albaugh was not sure about a 737 re-engine, like Boeing CFO James A. Bell stated at the JP Morgan Aviation, Transportation and Defense conference the same month. The A320neo gathered 667 commitments at the June 2011 Paris Air Show for a backlog of 1,029 units since its launch, setting an order record for a new commercial airliner.
On July 20, 2011, American Airlines announced an order for 460 narrowbody jets including 130 A320ceos and 130 A320neos, and intended to order 100 re-engined 737s with CFM LEAPs, pending Boeing confirmation. The order broke Boeing's monopoly with the airline and forced Boeing into a re-engined 737. As this sale included a Most-Favoured-Customer Clause, Airbus has to refund any difference to American if it sells to another airline at a lower price, so the European manufacturer can not give a competitive price to competitor United Airlines, leaving it to a Boeing-skewed fleet.
737 MAX 9 mockup at 2012 ILA Berlin
On August 30, 2011, Boeing's board of directors approved the launch of the re-engined 737, expecting a fuel burn 16% lower than the Airbus A320ceo and 4% lower than the A320neo. Studies for additional drag reduction were performed during 2011, including revised tail cone, natural laminar flow nacelle, and hybrid laminar flow vertical stabilizer. Boeing abandoned the development of a new design. Boeing expected the 737 MAX to meet or exceed the range of the Airbus A320neo. Firm configuration for the 737 MAX was scheduled for 2013.
In March 2010, the estimated cost to re-engine the 737 according to Mike Bair, Boeing Commercial Airplanes' vice president of business strategy & marketing, would be $2–3 billion including the CFM engine development. During Boeing's Q2 2011 earnings call, former CFO James Bell said the development cost for the airframe only would be 10–15% of the cost of a new program estimated at $10–12 billion at the time. Bernstein Research predicted in January 2012 that this cost would be twice that of the Airbus A320neo.
Fuel consumption is reduced by 14% from the 737NG. In November 2014, Boeing Chief Executive Officer Jim McNerney said the 737 will be replaced by a new airplane by 2030, slightly bigger and with new engines but keeping its general configuration, probably a composite airplane.
Boeing 737 MAX roll-out in December 2015 with the first 737 MAX 8
On August 13, 2015, the first 737 MAX fuselage completed assembly at Spirit Aerosystems in Wichita, Kansas, for a test aircraft that would eventually be delivered to launch customer Southwest Airlines. On December 8, 2015, the first 737 MAX—a MAX 8 named Spirit of Renton—was rolled out at the Boeing Renton Factory.
Because GKN could not produce the titanium honeycomb inner walls for the thrust reversers quickly enough, Boeing switched to a composite part produced by Spirit to deliver 47 MAXs per month in 2017. Spirit supplies 69% of the 737 airframe, including the fuselage, thrust reverser, engine pylons, nacelles, and wing leading edges.
A new spar-assembly line with robotic drilling machines should increase throughput by 33%. The Electroimpact automated panel assembly line sped up the wing lower-skin assembly by 35%. Boeing planned to increase its 737 MAX monthly production rate from 42 planes in 2017 to 57 planes by 2019.
The rate increase strained the production and by August 2018, over 40 unfinished jets were parked in Renton, awaiting parts or engine installation, as CFM engines and Spirit fuselages were delivered late. After parked airplanes peaked at 53 at the beginning of September, Boeing reduced this by nine the following month, as deliveries rose to 61 from 29 in July and 48 in August.
In collaboration with Commercial Aircraft Corporation of China Ltd., Boeing has built a completion and delivery facility for the 737 MAX in Zhoushan, China. This facility initially handles interior finishing only, but will subsequently be expanded to include paintwork. The first aircraft was delivered from the facility to Air China on December 15, 2018.
The first flight took place on January 29, 2016, at Renton Municipal Airport—nearly 49 years after the maiden flight of the 737, a 737-100, on April 9, 1967. The first MAX 8, 1A001, was used for aerodynamic trials: flutter testing, stability and control, and takeoff performance-data verification, before it was modified for an operator and delivered. 1A002 was used for performance and engine testing: climb and landing performance, crosswind, noise, cold weather, high altitude, fuel burn and water-ingestion. Aircraft systems including autoland were tested with 1A003. 1A004, with an airliner layout, flew function-and-reliability certification for 300h with a light flight-test instrumentation.
The 737 MAX gained FAA certification on March 8, 2017. It was approved by the EASA on March 27, 2017. After completing 2,000 test flight hours and 180-minute ETOPS testing requiring 3,000 simulated flight cycles in April 2017, CFM International notified Boeing of a possible manufacturing quality issue with low pressure turbine (LPT) discs in LEAP-1B engines. Boeing suspended 737 MAX flights on May 4, and resumed flights on May 12.
During the certification process, the FAA delegated many evaluations to Boeing, allowing the manufacturer to review their own product. It was widely reported that Boeing pushed to expedite approval of the 737 MAX to compete with the Airbus A320neo. That aircraft hit the market nine months ahead of Boeing's model.
The first delivery was a MAX 8, handed over to Malindo Air (a subsidiary of Lion Air) on May 16, 2017; it entered service on May 22. Norwegian Air subsidiary Norwegian Air International was the second airline to put a 737 MAX into service, when it performed its first transatlantic flight with a MAX 8 named Sir Freddie Laker on July 15, 2017 between Edinburgh Airport in Scotland and Bradley International Airport in the US state of Connecticut, followed by a second rotation from Edinburgh to Stewart Airport, New York.
Boeing aims to match the 99.7% dispatch reliability of the 737 Next Generation (NG). Southwest Airlines, the launch customer, took delivery of its first 737 MAX on August 29, 2017. Boeing planned to deliver at least 50 to 75 aircraft in 2017, 10–15% of the more than 500 737s to be delivered in the year.
After one year of service, 130 MAXs had been delivered to 28 customers, logging over 41,000 flights in 118,000 hours and flying over 6.5 million passengers. flydubai observed 15% more efficiency than the NG, more than the 14% promised, and dependability reached 99.4%. Long routes include 24 over 2,500 nmi (4,630 km), including a daily Aerolineas Argentinas service from Buenos Aires to Punta Cana over 3,252 nmi (6,023 km).
On March 11, 2019, in response to the Lion Air and subsequent Ethiopian Airlines accidents  Over the next two days, individual airlines and government authorities around the world also suspended operation of the aircraft, in contrast to the usual coordinated approach. Two days later, having initially resisted requests, the Federal Aviation Administration grounded the aircraft in the U.S. as the last aviation regulator to take action. Boeing, after resisting initial requests, then changed its mind and recommended the grounding to the FAA. As of March 14, 2019 , Boeing suspended deliveries of new aircraft, but continued production. European and Canadian regulators will conduct their own safety assessments independently of the FAA before lifting the grounding order.
, China ordered the grounding of all 737 MAX aircraft operated by its airlines.
The 737 MAX's Maneuvering Characteristics Augmentation System  Experts suggested that pilot training on the MCAS was insufficient.
was implicated in the Lion Air accident and came under suspicion due to apparent similarities in the Ethiopian Airlines crash.
The day after the Ethiopian Airlines crash, a subpoena was issued by a US grand jury. On March 19, 2019, the Department of Transportation requested the Office of Inspector General to conduct an audit on the 737 MAX certification process and Congress also announced an investigation into the same process. The FBI has joined the criminal investigation into the certification as well.