The Aero L-39 Albatros is a high-performance jet trainer designed and produced by Aero Vodochody in the Czech Republic. In addition to performing basic and advanced pilot training, it has also flown combat missions in a light-attack role. Despite its manufacturing origin in the Warsaw Pact, the L-39 never received a NATO reporting name.

The L-39 Albatros was designed during the 1960s as a successor to the Aero L-29 Delfín, an early jet-powered principal training aircraft. Performing its maiden flight on 4 November 1968, it became the first trainer aircraft in the world to be equipped with a turbofan powerplant. Quantity production of the L-39 Albatros proceeded in 1971; one year later, it was formally recognized by the majority of the Warsaw Pact countries as their preferred primary trainer. Accordingly, thousands of L39s would be produced for various military customers in Eastern Europe. Additionally, it was exported to a range of countries across the world both as a trainer and a light-attack aircraft. Since the 1990s, it has also become popular among civilian operators. By the end of the century, in excess of 2,800 L-39s had served with over 30 air forces.

Several derivatives of the L-39 Albatros were developed. During the 1980s, Aero Vodochody used it as the basis for the L-59 Super Albatros, an enlarged and updated model. Furthermore, the L-39 lineage would be extended to the L-139, a prototype L-39 fitted with a Western-sourced Garrett TFE731 engine. A combat-oriented development of the aircraft, designated as the L-159 ALCA, entered production in 1997, and has since been procured by a range of export customers. Production of the original L-39 came to an end during the mid-1990s, orders having declined substantially following the end of the Cold War. At the Farnborough Airshow in July 2014, Aero Vodochody announced the launch of the L-39NG, an upgraded and modernised version of the L-39; this programme is set to produce new-build aircraft alongside the extensive rebuilding of existing aircraft. In 2023, production of the L-39NG resumed under the name Skyfox, with 34 aircraft on order.

In 1964, the Czechoslovak aircraft manufacturer Aero Vodochody embarked on a new design project to meet the specified requirements for a "C-39" (C for cvičný – trainer), setting up a design team under the leadership of Jan Vlček [cs]. This aircraft was to serve as a replacement for the Aero L-29 Delfín, an early jet-powered trainer, as a principal training aircraft. Vlcek envisioned the type, a twin-seat single-engine aircraft, being adopted as the primary trainer throughout the Warsaw Pact nations.

On 4 November 1969, the L-39 (under the designation "Prototype X-02" – the second airframe to be built) conducted its maiden flight, for which it was piloted by Rudolf Duchoň, the factory's test pilot. Serial production of the initial model of the L-39, designated L-39C, commenced in 1971. During 1972, the L-39 Albatros was formally recognized by the majority of the countries comprising the Warsaw Pact as their preferred primary trainer, after which point, sizable orders from military customers throughout the bloc proceeded, many of which were from the Soviet Air Forces. In 1974, the first L-39 trainer entered service with the Czechoslovak Air Force.

Several specialised variants of the base L-39 design were quickly introduced. In 1972, a purpose-built target tug variant, the L-39V, conducted its initial flight. During 1975, the first L-39ZO training/light combat model, which was equipped with four underwing hardpoints as well as a strengthened wing and modified landing gear, performed its first flight. In 1977, the first L-39ZA light combat variant, which was fitted with a single Gryazev-Shipunov GSh-23 cannon mounted underneath the fuselage in addition to the four hardpoints and strengthening of the L-39ZO, made its maiden flight.

According to aerospace publication Flight International, roughly 200 L-39s were being sold each year in the jet trainer market during the late 1980s. According to the Stockholm International Peace Research Institute, in 1993, the total export orders gained for the L-39 represented 80 per cent of the value of all Czech military product export sales made for that year. During the 1990s, shortly following the dissolution of the Soviet Union and the end of the Cold War, Aero Vodochody decided to develop versions of the Albatros equipped with Western-sourced avionics, engines, and weapon systems. Around the same time, Aero Vodochody formed an active partnership with Elbit Systems of Israel, under which a number of L-39s were delivered to Elbit to be equipped with modern electronics and onboard systems before being re-exported to end users such as the Royal Thai Air Force.

Sales of the L-39 declined during the 1990s. This downturn has been attributed to the loss of the captive Warsaw Pact trainer market, to which a substantial proportion of the total aircraft manufactured had been historically sold; allegations about Czechoslovak banks being unable to finance the defense industry and inaction on the part of the Czechoslovak government; and concerns over the quality of manufacturing standards. In 1996, production of the L-39 came to an end. Since the end of production, Aero Vodochody has developed several improved variants of the L-39 to take its place, and has continued extensive support and overhaul operations for existing L-39 customers.