The world's largest-ever trial of a four-day workweek and reduced working time in Iceland was an "overwhelming success." The trials took place from 2015 to 2019 and involved about 2,500 workers, which represents 1 percent of Iceland's working population. Joint analysis by think tanks in Iceland and the UK found that the trials boosted productivity and wellbeing and are already leading to permanent changes. Icelandic trade union federations, which collectively negotiate wages and conditions for most Icelandic employees, have already begun to negotiate for reduced working hours as a result. Researchers estimate that as a result of the new agreements, struck in 2019-'21 after the trials ended, 86 percent of Iceland's entire working population now either have reduced hours or flexibility within their contracts to reduce hours.