Joan Mary Waller Greenwood (4 March 1921 – 28 February 1987) was an English actress. Her husky voice, coupled with her slow, precise elocution, was her trademark. She is perhaps best remembered for her role as Sibella in Kind Hearts and Coronets (1949). Her other film appearances included The Man in the White Suit (1951), The Importance of Being Earnest (1952), Stage Struck (1958), Tom Jones (1963) and Little Dorrit (1987).
Greenwood was born in 1921 in Chelsea, London. Her parents were Ida (née Waller) and Sydney Earnshaw Greenwood (1887–1949), a portrait artist. Her education included studies at the Royal Academy of Dramatic Art.
Greenwood worked mainly on the stage, where she had a long career, appearing with Donald Wolfit's theatre company in the years following World War II. Later, after the war, her appearances in Ealing comedies are among her memorable screen appearances: Whisky Galore!; as the seductive Sibella in the black comedy Kind Hearts and Coronets (1949); and in The Man in the White Suit (1951). She opened The Grass Is Greener in the West End in 1952 and played Gwendolyn in a film version of The Importance of Being Earnest released in the same year.