According to the co-writer and longtime band member Bob Gaudio, the song was originally set in 1933 with the title "December 5th, 1933," and celebrated the repeal of Prohibition. Neither lead singer Frankie Valli nor co-writer (and Gaudio's wife) Judy Parker were thrilled about the lyrics - and Valli objected to parts of the melody - so Gaudio redid the words and Parker redid the melody until all were content with the finished product. It ended up being a nostalgic love song.
The group had to play down the sexual overtones in this song to appease conservative radio stations, but lead singer Frankie Valli later admitted that the song was "about losing your cherry" - a guy having sex for the first time. It's a similar theme to the Shirelles hit "Will You Love Me Tomorrow
The lead singer on the first verse was their drummer Gerri Polci - Frankie Valli comes in on the second verse. As well as sharing the lead in "December 1963," Polci was the lead singer on the group's third hit from the Who Loves You LP, "Silver Star," which hit #38 in the US.
Their fifth and final #1 hit in the US, this was the only Four Seasons recording to top the UK charts.
The Four Seasons had a series of hits from 1962-1968. In 1975, they returned to the charts with "Who Loves You," which hit #3 in the US. "December 1963" was the follow-up to that song.
A dance remix version hit #14 US in 1994, introducing the song to a new generation. The remix stayed in the Top 40 for a stunning 20 weeks, and if combined with the 15 weeks the original spent on the chart, the song has had the longest stay on the Top 40. Valli, however, is not a fan of the new version. He told Billboard: "I'll never like it better than when it was pure."
When this hit US #1 in 1976, it made The Four Seasons the only artist in history to have #1 songs before (several), during ("Rag Doll") and after the Beatles. (thanks, Dan - Buffalo, NY)
This was used in the 1994 movie Forrest Gump, and the song was re-released as part of the soundtrack. It once again entered the charts, and became the longest-running single in the Billboard US chart's history, with over 50 weeks total.
December, 1963 was one of the less celebratory months in American history. President John F. Kennedy was assassinated on November 22, 1963.