"It's The Most Wonderful Time Of The Year" is a collaboration by composer George Wyle (known for writing the Gilligan's Island theme) and his regular partner Eddie Pola. It was written specifically for The Andy Williams Christmas Album and the crooner performed it on his popular variety show, The Andy Williams Show. He went on to record seven more Christmas albums, and this song appeared on every one of them. The song's popularity, paired with the singer's penchant for gaudy sweaters and holiday TV specials, earned him the nickname "Mr. Christmas."

Surprisingly, this song was not released as the promotional single for the album. Columbia Records decided to release Williams' cover of Bing Crosby's "White Christmas," instead. It topped the special Billboard Christmas Singles chart and was the #1 selling Christmas single.

Williams recorded this song as a duet with Contemporary Christian music singer Kathy Troccoli in 1999.

Over the years, this song has become an enduring holiday standard with covers by several artists for their Christmas albums, including Johnny Mathis, Amy Grant, Vince Gill, Garth Brooks, Paul Anka, and Chicago, to name a few. Harry Connick Jr.'s version for his What a Night! A Christmas Album, peaked at #9 on the Billboard Hot Adult Contemporary Tracks chart.

This song is featured Home Alone 2: Lost in New York (1992) as an ironic aside when Kevin McCallister's family starts their Florida vacation in a downpour outside of a seedy motel.

The song entered the Hot 100 Top 10 for the first time when it landed at #10 on the chart dated December 29, 2018. It was Williams' first Top 10 hit since 1971's "(Where Do I Begin) Love Story." The 47 years, eight months and three days between his two visits to the upper reaches of the tally broke the record for the longest time span between US Top 10 appearances.

Andy Williams' record was broken just one week later when Burl Ives' "Holly Jolly Christmas" moved into the top ten for the first time. It was his top 10 entry since "Funny Way Of Laughin'" peaked at #10 in 1962, 56 and a half years previously.