William Say (1604–c.1666) was an English politician.

William Say may also refer to:

• William Say (priest), (died 1468), English priest, Dean of the Chapel Royal and Dean of St Paul's
• William Say (MP for New Shoreham), English MP for New Shoreham (UK Parliament constituency), 1452
• William Say (MP), English MP for New Shoreham (UK Parliament constituency), 1491, 1495
• William Say (engraver), b.1768

• Appellate procedure in the United States
• Appellate review
• Appellation
• Appellation controlée
• Appellation d'origine contrôlée
• Appellation d’Origine Contrôlée
• Appellation of origin
• Appellations
• Appellee
• Appell sequence
• Appel reaction
• Appel sequence
• Appel sequences
• Appendage
• Appendages
• Appendectomies
• Appendectomy
• Appendicitis
• Appendicularia
• Appendicular skeleton
• Appendicular Skeleton
• Appendix
• Appendix (anatomy)
• Appendix (horse)
• Appendix (organ)