Judgement Day is an annual Welsh Rugby Union event that takes place at Millennium Stadium in Cardiff and is part of the United Rugby Championship competition. The four regions – Cardiff Rugby, Dragons, Ospreys and Scarlets – join with the Welsh Rugby Union in organising a double-header fixture at the Millennium Stadium. The annual derby day clash will be repeated in the foreseeable future, with the two east Wales regions taking on the two west Wales regions. In 2020, the two matches were held on consecutive days at Rodney Parade due to the COVID-19 pandemic causing a change to the format of the 2019–20 season and the Millennium Stadium being unavailable due to it being used as the Dragon's Heart Hospital.

The Millennium Stadium, known since 2016 as the Principality Stadium for sponsorship reasons, is the national stadium of Wales. Located in Cardiff, it is the home of the Wales national rugby union team and has also held Wales national football team games. Initially built to host the 1999 Rugby World Cup and replacing the National Stadium, it has gone on to host many other large-scale events, such as the Tsunami Relief Cardiff concert, the Super Special Stage of Wales Rally Great Britain, the Speedway Grand Prix of Great Britain and various concerts. It also hosted FA Cup, League Cup and Football League play-off finals while Wembley Stadium was being redeveloped between 2001 and 2006, as well as football matches during the 2012 Summer Olympics.