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

The song was originally written for Labelle (a trio led by Patti LaBelle) but they never recorded it. Much like the issue with "I Miss You" and The Dells passing on it, the song's composers Kenny Gamble and Leon Huff gave the song to Harold Melvin & the Blue Notes, which featured Teddy Pendergrass as lead vocalist. In addition to the single release, the song was included on their debut album I Miss You.

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

It was later covered by the English pop/soul band Simply Red, also becoming their second best-known hit after reaching number one on the U.S. Hot 100 on July 15, 1989, and at number thirty-eight on the Hot Black Singles chart. It peaked at number two in the UK Singles Chart. It also topped the Canadian Singles Chart.

Seal recorded the song for his 2008 album Soul, and, in April 2009, it became his first top-ten Adult Contemporary hit since "Love's Divine" in 2004; the song was subsequently nominated for the Best Male Pop Vocal Performance Grammy.

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