Juliet Maryon Mills (born 21 November 1941) is a British and American actress. She is the daughter of actor Sir John Mills and Mary Hayley Bell and the eldest of three siblings; her younger siblings are actress Hayley Mills and director Jonathan Mills.

Mills began her career as a child actress and was nominated for a Tony Award for her stage performance in Five Finger Exercise in 1960. She progressed to film work and then to television, playing the lead role on the sitcom Nanny and the Professor in 1970–71. She received Golden Globe Award nominations for her work in this series and for her role in the film Avanti! in 1972. She won an Emmy Award for her performance in the television miniseries QB VII (1974). In 1983, Mills joined The Mirror Theater Ltd's Mirror Repertory Company, performing in repertory productions such as Rain, Paradise Lost, Inheritors and The Hasty Heart throughout their seasons.

From 1999 until 2008, she had a role on the daytime drama series Passions, for which she was nominated for a Daytime Emmy Award. From 28 May 2015, Mills toured Australia with her husband Maxwell Caulfield and her sister Hayley Mills in the comedy Legends! by James Kirkwood.