Written and first recorded (as an instrumental demo) by K.C. & The Sunshine Band (1974).
Hit version by George McCrae (US #1/R&B #1/UK #1/AUS #1 1974).
From the wiki: “‘Rock Your Baby’ was written and produced by Harry Wayne Casey (‘K.C.’) and Richard Finch of K.C. & The Sunshine Band, and is considered to be one of the landmark recordings of early disco music.
“The backing track for the record had been recorded in 45 minutes as a demo, and featured guitarist Jerome Smith, saxophonist Whit Sidener and trumpeter Vinnie Tanno of K.C. & The Sunshine Band. The track was not originally intended for McCrae. But, he happened to be in the studio, was invited by K.C. to add a vocal, and the resulting combination of infectious rhythm and falsetto vocal made it a hit. An instrumental re-recording would later be released as a separate single, in 1975 in the US (backed with ‘S.O.S.’) and in 1976 in the UK (backed with ‘Sunshine City’).