The Mi-26 was designed to replace earlier Mi-6 and Mi-12 heavy lift helicopters and act as a heavy-lift helicopter for military and civil use, having twice the cabin space and payload of the Mi-6, then the world's largest and fastest production helicopter. The primary purpose of the Mi-26 was to transport military equipment such as 13-metric-ton (13,000 kg; 29,000 lb) amphibious armored personnel carriers and mobile ballistic missiles to remote locations after delivery by military transport aircraft such as the Antonov An-22 or Ilyushin Il-76.
The first Mi-26 flew on 14 December 1977 and the first production aircraft was rolled out on 4 October 1980. Development was completed in 1983 and by 1985, the Mi-26 was in Soviet military and commercial service.
Aeroflot Mi-26 at the 1984 Farnborough Air Show
The Mi-26 was the first factory-equipped helicopter with a single, eight-blade main lift rotor. It is capable of flight in the event of power loss by one engine (depending on aircraft mission weight) because of an engine load sharing system. While its empty weight is only slightly higher than the Mi-6's, the Mi-26 has a payload of up to 20 metric tons (20,000 kg; 44,000 lb). It is the second largest and heaviest helicopter ever constructed, after the experimental Mil V-12. The tail rotor has about the same diameter and thrust as the four-bladed main rotor fitted to the MD Helicopters MD 500.
The Mi-26's unique main gearbox is relatively light at 3,639 kg (8,023 lb) but can absorb 19,725 shaft horsepower (14,709 kW), which was accomplished using a non-planetary, split-torque design with quill shafts for torque equalization. The Mil Design Bureau designed the VR-26 transmission itself, due to the normal gearbox supplier used by Mil admitting that it could not design such a gearbox. The gearbox housing is stamped aluminum. A split-torque design is also used for the 5,670 kg (12,500 lb) gearbox on the American three-engine Sikorsky CH-53K King Stallion.
In July 2010 a proposed Russian-Chinese development of a 33-ton heavy-lift helicopter was announced. In early 2019, Russia's state corporation Rostec inked a landmark agreement on developing a 40-ton next-generation heavy helicopter. 
Rostvertol, the Russian helicopter manufacturer, was contracted to refurbish and upgrade the entire fleet of Mi-26s serving in the Russian Air Force, estimated to be around 20 helicopters. The upgraded aircraft is comparable to a new variant, the Mi-26T. Contract completion was planned for 2015. The contract also covered the production of 22 new Mi-26T helicopters. Eight new-built helicopters were delivered to operational units by January 2012. Under the 2010 contract, 17 new-production helicopters were delivered by 2014. In all, Rostvertol delivered fourteen Mi-26s to domestic and foreign customers in the period 2012‑14 and six helicopters in 2015. Deliveries to the Russian Air Force were continued in 2016, 2017 and 2019.
In 2016, Russia started development of PD-12V a variant of the Aviadvigatel PD-14 turbofan engine to power the Mi-26.
A Mi-26 in a military parade over Caracas, Venezuela
The Mi-26S was a disaster response version hastily developed during the containment efforts of the Chernobyl nuclear accident in 1986. Thirty Mi-26 were used for radiation measurements and precision drops of insulating material to cover the damaged No.4 reactor. It was also equipped with a deactivating liquid tank and underbelly spraying apparatus. The Mi-26S was operated in immediate proximity to the nuclear reactor, with a filter system and protective screens mounted in the cabin to protect the crew during delivery of construction materials to the most highly contaminated areas.
Siberian Woolly Mammoth recovery
In October 1999, an Mi-26 was used to transport a 25-ton block of frozen soil encasing a preserved, 23,000-year-old woolly mammoth (Jarkov Mammoth) from the Siberian tundra to a lab in Khatanga, Taymyr. Due to the weight of the load, the Mi-26 had to be returned to the factory afterward to check for airframe and rotor warping caused by the potential of structural over-stressing.
Afghanistan Chinook recovery
In early 2002, a civilian Mi-26 was leased to recover two U.S. ArmyMH-47E Chinook helicopters from a mountain in Afghanistan. The Chinooks, operated by the 160th Special Operations Aviation Regiment, had been employed in Operation Anaconda, an effort to drive al Qaeda and Taliban fighters out of the Shahi-Kot Valley and surrounding mountains. They found themselves stranded on the slopes above Sirkhankel at altitudes of 2,600 metres (8,500 ft) and 3,100 metres (10,200 ft). While the second craft was too badly damaged to recover, the first was determined to be repairable and estimated to weigh 12,000 kilograms (26,000 lb) with fuel, rotors, and non-essential equipment removed. That weight exceeded the maximum payload of 9,100 kilograms (20,100 lb) at an altitude of 2,600 metres (8,500 ft) of the U.S. military's Sikorsky CH-53E.
The Mi-26 was located through Skylink Aviation in Toronto, which had connections with a Russian company called Sportsflite that operated three civilian Mi-26 versions called "Heavycopters". One of the aircraft, aiding in construction and firefighting work in neighboring Tajikistan, was leased for $300,000; it lifted the Chinook, flew it to Kabul, then later to Bagram Air Base, Afghanistan to ship to Fort Campbell, Kentucky, U.S. for repairs. Six months later, a second U.S. Army CH-47 that had made a hard landing 160 kilometres (100 mi) north of Bagram at an altitude of 1,200 metres (3,900 ft) was recovered by another Sportsflite-operated Mi-26 Heavycopter.
In July 2009, a Moldovan Mi-26 was shot down in Helmand province with the loss of six Ukrainian crew members. The aircraft, belonging to Pecotox Air, was said to be on a humanitarian mission under NATO contract.
Indian Air Force Mi-26 crash
On 14 December 2010, an Indian Air Force Mi-26 crashed seconds after taking off from Jammu Airport, injuring all nine passengers. The aircraft fell from an altitude of about 15 metres (50 ft). The Indian Institute of Flight Safety released an investigation report that stated improper fastening of the truck inside caused an imbalance of the helicopter and led to the crash. The Mi-26 had been carrying machines from Konkan Railway to Jammu-Baramulla line project.
Norwegian Air Force Sea King recovery
On 11 December 2012, a Westland Sea King from No. 330 Squadron RNoAF experienced undisclosed technical issues and made an emergency landing on Mount Divgagáisá. The landing caused parts of the landing gear to break. The Sea King was prepared by removing rotor blades and fuel before it was airlifted to Banak Air Station by a Russian Mil Mi-26 on 23December 2012.
Improved version of the Mi-26T equipped with BREO-26 airborne electronic system, allowing it to fly any time, day or night, under good and bad weather conditions. Serial production began on May 22, 2015.
Newest modernization variant intended for the Russian military, equipped with new NPK90-2V avionics suite allowing it to fly routes in automatic mode, airborne defense complex "Vitebsk", anti-blast seats and new navigation and satellite communication systems. The cockpit is fitted with multifunctional displays with provision for use of night-vision goggles during night ops. The Mi-26T2V made its maiden flight in August 2018.
Proposed airborne command post variant; two prototypes built.