Still Canada's most successful commercial aircraft program with more than 800 built, the Twin Otter remains popular for its rugged construction and useful STOL performance.

Development of the Twin Otter dates back to January 1964 when De Havilland Canada started design work on a new STOL twin turboprop commuter airliner (seating between 13 and 18) and utility transport. The new aircraft was designated the DHC-6 and prototype construction began in November that year, resulting in the type's first flight on May 20 1965. After receiving certification in mid 1966, the first Twin Otter entered service with long time De Havilland Canada supporter the Ontario Department of Lands in Canada.

The first production aircraft were Series 100s. Design features included double slotted trailing edge flaps and ailerons that can act in unison to boost STOL performance. Compared with the later Series 200s and 300s, the 100s are distinguishable by their shorter, blunter noses.

The main addition to the Series 200, which was introduced in April 1968, was the extended nose, which, together with a reconfigured storage compartment in the rear cabin, greatly increased baggage stowage area.

The Series 300 was introduced from the 231st production aircraft in 1969. It too featured the lengthened nose, but also introduced more powerful engines, thus allowing a 450kg (1000lb) increase in takeoff weight and a 20 seat interior. Production ceased in late 1988. In addition, six 300S enhanced STOL performance DHC-6-300s were built in the mid 1970s.