The Chengdu J-20 (Chinese: 歼-20; pinyin: Jiān-Èrlíng), also known as Weilong (Chinese: 威龙; pinyin: Wēilóng; lit. 'Mighty Dragon', NATO reporting name: Fagin), is a twin-engine all-weather stealth fighter developed by China's Chengdu Aircraft Corporation for the People's Liberation Army Air Force (PLAAF). The J-20 is designed as an air superiority fighter with precision strike capability. The aircraft has three notable variants: the initial production model, the revised airframe variant with new engines and thrust-vectoring control, and the aircraft-teaming capable twin-seat variant.

Descending from the J-XX program of the 1990s, the aircraft made its maiden flight on 11 January 2011, and was officially revealed at the 2016 China International Aviation & Aerospace Exhibition. The aircraft entered service in March 2017 with the first J-20 combat unit formed in February 2018, making China the second country in the world to field an operational stealth aircraft.

The J-20 emerged from the late-1990s J-XX program. Chengdu had previously used the double-canard configuration in the J-9, its first design and cancelled in the 1970s, and the J-10. The general configuration of Chengdu's J-XX design was first published internally in a 2001 Chengdu paper authored by Song Wencong that describes the advantages of an unstable canard and LERX configuration. In 2008, the PLAAF endorsed Chengdu Aircraft Corporation's proposal, Project 718.

In 2009, a senior PLAAF official revealed that the first flight was expected in 2010–11, with a service entry date by 2019. On 22 December 2010, the first J-20 prototype underwent high speed taxiing tests outside the Chengdu Aircraft Design Institute (CADI). Three months later, the first J-20 prototype made its maiden flight in Chengdu. The first prototype was painted with the number "2001". In May 2012, the second prototype took flight in the CADI facility.

Several changes were made to the third J-20 prototype, numbered "2011", which made its maiden flight in March 2014. The new prototype showed increasing sophistication in design, including numerous subtle changes from the first two prototypes. The new airframe introduced modified diverterless supersonic inlet (DSI) intakes, stealth coating, streamlined underwing fairings, and redesigned vertical stabilizers. Analysts noted new equipment and devices for multi-role operations, such as integrated targeting pods for precision-guided munition, and six additional passive infrared sensors can also be spotted around the aircraft.

In December 2015, the low rate initial production (LRIP) version of the J-20 was spotted by military observers.

In October 2017, Chinese state media reported that the designs of the J-20 had been finalized, and were ready for mass production as well as being combat-ready. In March 2018, Chinese military revealed other versions of the J-20 platform were being developed.

In January 2019, Chinese media reported that a twin-seat variant of the J-20 is rumored to be in development for use in tactical bombing, electronic warfare and carrier strike roles.