John Klenner (24 February 1899 – 13 August 1955) was a German-born American pianist, composer, and lyricist renowned for his contributions to both classical and popular music. He is best known for the song "Just Friends," which he co-wrote with Sam M. Lewis in 1931. This song, originally a pop ballad, later became a jazz standard, recorded by notable artists such as Charlie Parker, Chet Baker, Sarah Vaughan, and Bill Evans.

Klenner's body of work includes a variety of compositions, ranging from concertante pieces like "Fantasia for viola and orchestra" to numerous vocal works. Some of his notable songs include "Japansy" and "My Window of Dreams," both written around 1928 with Alfred Bryan, as well as "Down the River of Golden Dreams" (1930), "Heartaches" (1931), and "Round the Bend of the Road" (1932). In 1942, he composed "On the Street of Regret," and in 1947, he provided lyrics for "Summer Moon," an adaptation of a piece from Igor Stravinsky's "The Firebird."

Klenner's music continues to be celebrated for its melodic richness and emotional depth, contributing significantly to the American musical landscape of the early to mid-20th century.