"I'm a Believer" is a song composed by Neil Diamond and recorded by The Monkees in 1966 with the lead vocals by Micky Dolenz. The single, produced by Jeff Barry, hit the number one spot on the U.S. Billboard Hot 100 chart for the week ending December 31, 1966 and remained there for seven weeks, becoming the last No. 1 hit of 1966 and the biggest-selling record for all of 1967. Billboard ranked the record as the No. 5 song for 1967. Because of 1,051,280 advance orders, it went gold within two days of release. It is one of the fewer than forty all-time singles to have sold 10 million (or more) physical copies worldwide.

The song was No. 1 in the UK Singles Chart for four weeks in January and February 1967, as well as a Number 1 in numerous countries including Australia, Canada, and Ireland.

The success of the single prompted the song to appear in four consecutive episodes of The Monkees' TV show throughout December 1966.

Neil Diamond had already recorded this song before it was covered by The Monkees, and it still sometimes appears in his live concerts. A revised recording by Diamond, featuring additional lyrics, appears on the album September Morn, while his original recording appeared on the 1967 album Just for You. Diamond also suggested it to The Fifth Estate who recorded it as a 1967 album cut to follow up their hit "Ding-Dong! The Witch Is Dead". The Monkees' recording kept the novelty hit "Snoopy Vs. The Red Baron", by The Royal Guardsmen, at number two for four weeks, and from reaching the Hot 100's summit.

The song was originally used in the home video version of the Coen brothers' 1984 film Blood Simple, but after licensing issues were resolved, was replaced in the 2001 director's cut by the song used in the theatrical version: Four Tops' "It's the Same Old Song".

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