Willem de Sitter (1872–1934) was a Dutch mathematician, physicist and astronomer.
De Sitter may also refer to: De Sitter (crater), a lunar crater 1686 De Sitter, an asteroid
People with the surname Ulbo de Sitter (1902–1980), Dutch geologist Ulbo de Sitter (sociologist) (1930–2010), Dutch sociologist whose work has been further developed by Jan in 't Veld
See also De Sitter space and anti-de Sitter space, models of spacetime De Sitter universe, a solution to general relativity De Sitter effect (disambiguation) Sitter (disambiguation)