Joanna Elizabeth Simon, oldest sister of singer Carly Simon, was an American mezzo-soprano and TV journalist. As a singer, Simon was known for possessing a distinctively "smoky-voiced mezzo-soprano". She performed regularly in operas and concerts internationally from 1962 through 1986, and thereafter made only periodic performances into the late 1990s.

In 1962, she won the regional division of the Metropolitan Opera National Council Auditions and the Marian Anderson Award, also making her opera debut that year at the New York City Opera as Mozart's Cherubino. She created the role of Pantasilea in the world premiere of Alberto Ginastera's Bomarzo in 1967 with the Washington Opera Society (now the Washington National Opera), which brought her international fame, and she recorded the part for CBS Records.

She was the first singer to record the role of Irene in Handel's Tamerlano; singing the part for the opera's first recording in 1970. She also made recordings with several orchestras during her career, including the New York Philharmonic, The Vienna Philharmonic, and the Pittsburgh Symphony Orchestra.

In 1972, she performed the title role in the world premiere of Thomas Pasatieri's Black Widow at the Seattle Opera, and in 1975 she performed the role of Pelagia in the world premiere of Robert Starer's The Last Lover at the Caramoor Music Festival.

On television she was a featured performer on the very last episode of The Ed Sullivan Show on March 28, 1971. She also was a panelist on What's My Line? (1968) and made appearances on programs hosted by Merv Griffin, Mike Douglas, Dick Cavett, and David Frost.

In 1984, she was a singer in the recording of her sister Carly's song "Turn of the Tide" which was commissioned by the Democratic Party for use in political campaigning, and she also performed as a backup singer on albums made by both of her sisters.

After mostly retiring from singing professionally in 1986, Simon worked as the arts correspondent for PBS's MacNeil-Lehrer News Hour from 1986 to 1992. She won an Emmy Award for her work with the program. She later worked as a real estate broker in Manhattan with the Fox Residential Group. Married to the novelist Gerald Walker from 1976 until his death in 2004, she was the companion of Walter Cronkite from 2005 until his death in 2009.

Simon died from thyroid cancer in Manhattan on October 19, 2022, a day before her 86th birthday, just one day before her younger sister Lucy died of breast cancer.