Roald Dahl Plass (Welsh: Plas Roald Dahl) is a public plaza in Cardiff Bay. It is named after Cardiff-born author Roald Dahl, and is located on the coast along the south of the city centre. The square is home to the Senedd (Welsh Assembly Building) and the Wales Millennium Centre, a performing arts centre. The bowl-like shape of the plaza has made it a popular amphitheatre for hosting open-air concerts.

Formerly named the Oval Basin, the area was one of the docks for a thriving coal port during the latter half the 19th century and much of the 20th century. Following World War II, the plaza entered a period of decay and dereliction until the 1980s, when the Cardiff Bay area was regenerated.