"Rock Around the Clock" (Jimmy DeKnight/Max C. Freedman) is a song by Bill Haley and His Comets, which was used as the main title music for the first two seasons of Happy Days. Originally recorded in April 1954, Haley recorded a new, slightly abbreviated version for use as the opening of Happy Days (he also re-recorded several other songs, including "See You Later Alligator", for the show). The syndicated version, Happy Days Again, uses an edited version of the original 1954 recording.

The original "Rock Around the Clock" was recognized by Guinness World Records as the highest-selling vinyl pop single, with estimated sales of 25 million, and is credited with officially starting the rock and roll craze when it hit No. 1 on charts around the world after its use in the 1955 film Blackboard Jungle. Prior to Happy Days, the song was used as the opening credits music for American Graffiti, starring Ron Howard. Due to its use in that film, and Happy Days, the original 1954 version was reissued by MCA Records and re-entered both the American and UK Top 40 charts in the spring of 1974.

As of 2017, the original Happy Days studio re-recordings have yet to be released; the early 1980s compilation Fonzie Favorites used the 1954 version. The only commercial release to date is an off-air recording of featured in the 2003 German release Bill Haley and Friends Vol. 3: The Story of Rock Around the Clock from Hydra Records.


The record label shown on the spinning record in the opening sequence is actually for the "Happy Days" theme song itself, with that song's writers visible, rather than the label reflecting the credits of "Rock Around the Clock".


One, Two, Three O'clock, Four O'clock rock,
Five, Six, Seven O'clock, Eight O'clock rock.
Nine, Ten, Eleven O'clock, Twelve O'clock rock,
We're gonna rock around the clock tonight.
Put your glad rags on and join me hon',
We'll have some fun when the clock strikes one.


We're gonna rock around the clock tonight,
We're gonna rock, rock, rock, 'till broad daylight,
We're gonna rock, we're gonna rock around the clock tonight.
When the clock strikes two, three and four,
If the band slows down we'll yell for more.


When the chimes
ring five, six, and seven,
We'll be right in seventh heaven.


When it's eight, nine, ten, eleven too,
I'll be going strong and so will you.


When the clock strikes twelve we'll cool off then,
Start rockin' 'round the clock again.