Stanley John Sadie, CBE (/ˈseɪdi/; 30 October 1930, Wembley – 21 March 2005, Cossington, Somerset) was an influential and prolific British musicologist, music critic, and editor. He was editor of the sixth edition of the Grove Dictionary of Music and Musicians (1980), which was published as the first edition of the New Grove Dictionary of Music and Musicians.
Sadie was educated at St Paul's School, London, and Gonville and Caius College, Cambridge, where he read music under Thurston Dart. Sadie earned a Bachelor of Arts and Bachelor of Music degrees in 1953, a Master of Arts degree in 1957, and a PhD in 1958. His doctoral dissertation was on mid-eighteenth-century British chamber music. After Cambridge, he taught at Trinity College of Music, London (1957–1965).
Sadie then turned to music journalism, becoming music critic for The Times (1964–1981), and contributing reviews to the Financial Times after 1981, when he had to leave his position and The Times because of his commitments to the Grove and other scholarly work. He was editor of The Musical Times 1967–1987.