Du-reformen (Swedish pronunciation: [ˈdʉ̂ːrɛˌfɔrmɛn]) was the process of popularization of the second-person singular pronoun du as a universal form of address in Sweden that took place in the late 1960s.
With exceptions in dialectal usage, the second-person plural pronoun Ni had long been considered degrading when used to address a single person.
In the Swedish of Sweden, the polite ni was known from earlier epochs, but had come to be considered careless, bullying or rude; instead, an intricate system had evolved in order to prudently step around pronouns almost altogether.
[1] The second person singular du was used only to and between children, within a married couple, between lovers or to a more or less voluntary mistress of lower standing, and between friends who had toasted for brotherhood with each other ('toasted for thou' in a "du-skål" as it was known)—of course initiated by the elder or higher-ranked party.
In the province of Dalarna, however, and in some other remote places with few upper-class people, the du/ni distinction had remained one of number only; although children addressed their parents with Father/Mother (Far/Mor) rather than a grammatically logical du.
In other remote places, the Ni survived in its older form I (cognate with 'ye') as both the second person plural pronoun and the polite address to singular elders, including one's parents, unless classified with "better people".
As the twentieth century progressed, this circumlocutive system of addressing, with its innumerable ambiguities and opportunities for unintentional offence, was increasingly felt as a nuisance.
The beginning of du-reformen is associated with Bror Rexed, the then head of the National Board of Health and Welfare (Socialstyrelsen), who in his welcome speech to the staff in 1967 announced that he would address everyone as du, increasing the effects of the reform and bringing it to a more frequent use.