"If You Don't Know Me by Now" is a song written by Kenny Gamble and Leon Huff, and recorded by the Philadelphia soul musical group Harold Melvin & the Blue Notes. It became their first hit after being released as a single in September 1972, topping the US R&B chart and peaking at number 3 on the US Billboard Hot 100.

"If You Don't Know Me by Now" was originally written for Labelle (a trio led by Patti LaBelle) but they never recorded it. The song's composers Kenny Gamble and Leon Huff gave it to Harold Melvin & the Blue Notes, which featured Teddy Pendergrass as lead vocalist, and the actual background vocals done by producers Kenny Gamble, Leon Huff, Carl Helm, and Bunny Sigler. In addition to the single release, the track was included on their debut album, I Miss You.

Patti LaBelle later made the song part of her concert repertoire in 1982; a live version appears on her 1985 album, Patti.

"If You Don't Know Me by Now" has since been recorded by a number of other artists, most notably the English pop and soul band Simply Red, who took their version to number one on the Billboard Hot 100 in 1989.

The song "If You Don’t Know Me By Now" was chosen as one of the "Songs of the Century" by the Recording Industry Association of America (RIAA).