About 70 companies, which involves some 3000 UK workers, are taking part in the experiment over the next six months.
During the trial, employees will get 100% pay for 80% of the hours they would usually work, with the aim of being more productive.
Academics from Oxford and Cambridge universities, as well as experts at Boston College in the US, will manage the experiment in partnership with the think tank Autonomy.
"The basis of this movement is that there's activity going on in many workplaces, particularly white collar workplaces, that's low-productivity and that you can cut without harming the business."
- Juliet Schor, Lead Researcher on the Global 4-day week project, and an Economist and Sociologist at Boston College
Companies ranging from office-based software developers and recruitment firms to charities and a local fish and chip shop are taking part.
"You'd have to become 25% more productive per day. There are some services where a four-day working week is not a realistic option. Doctors are already struggling to provide enough GP appointments - how can they see 25% more patients in a day? And it's difficult to see how a bar person can pull 25% more pints in a day too."
- Julian Jessop, Independent Economist and fellow at the Institute of Economic Affairs
