The Patriotic and Democratic Front of the Great National Union of Kampuchea (Khmer: រណសិរ្សប្រជាធិបតេយ្យស្នេហាជាតិនៃមហាសាមគ្គីជាតិកម្ពុជា) (PDFGNUK) was a Kampuchean mass organization set up by the Communist Party of Kampuchea (popularly known as the Khmer Rouge) on August 21, 1979^[1] after the fall of Democratic Kampuchea to Vietnamese troops and the subsequent proclamation of the People's Republic of Kampuchea. It was set up as a counterpart to the Kampuchean United Front for National Salvation that had been nurtured by the Vietnamese. Its purpose was to rally anti-Vietnamese nationalists to support the Khmer Rouge, as part of an effort to legitimize the discredited Democratic Kampuchea regime.^[2] It was announced by Khieu Samphan, who was elected its provisional chairman.^[3] The PDFGNUK can be seen as an attempt to revive the goals of the similar GRUNK coalition of the early 1970s, an organization that united the Khmer Rouge and pro-Sihanouk forces opposing the Khmer Republic.

In theory, the Union served as an interim organization fulfilling the conditions of a government in exile at the Kampuchean-Thai border until the formation of the Coalition Government of Democratic Kampuchea in 1982. Within a year the Front had published a draft of its political program. With Chinese backing it disowned some of the "errors" of the 1975-1979 period and announced that the ability to freely marry and to practice religion was to be respected,^[4] while also calling for a "liberal democratic system" replacing the 1976 constitution^[5][6] as it "renounced the building of socialism and communism for tens or hundreds of years in order to mobilize a broad national front to crush the Vietnamese enemy, the Lê Duẩn clique."^[7] The Front promoted calls for free, contested elections with UN oversight after the expulsion of Vietnamese troops^[8] and encouraged the development of private property along with the participation of hitherto persecuted Buddhist monks in the governing affairs of the country.^[9] These activities however were widely seen as having ulterior and dishonest motives, with Prince Sihanouk denouncing the Front and its program as a "ploy," and "only a few responded to the Khmer Rouge's appeal for unity under the PDFGNUK," though despite this the Front formally continued to exist as of 1987 under the Party of Democratic Kampuchea.^[10]