The series began as an unsold 1971 pilot titled 'New Family in Town', later recycled as 'Love and the Television Set' (retitled 'Love and the Happy Days'), a segment of the anthology series Love, American Style that aired in 1972.

The concept originated in late winter 1971 when Michael Eisner, snowed in at Newark airport, met Paramount development head Tom Miller and suggested they write a show together, even though market research indicated a 1950s-themed series would not work.

Director George Lucas watched the unsold Happy Days pilot to judge whether Ron Howard could convincingly play a teenager, and immediately cast him in American Graffiti (1973), whose success renewed ABC's interest in turning the pilot into a series.

Harold Gould originally played Howard Cunningham in the pilot, but after taking a play abroad during a production delay, he declined to return, so Tom Bosley was cast instead.

The role of Fonzie came down to a choice between Micky Dolenz (of The Monkees) and Henry Winkler, and Dolenz later said Winkler 'deserved it'.

Fonzie's leather jacket was initially resisted by ABC executives, who feared it made him look too much like a hoodlum, so he wore a light grey McGregor windbreaker in season one; that jacket was eventually thrown in the garbage once ABC allowed the leather jacket.

The first two seasons were filmed single-camera with a laugh track, but one season two episode, 'Fonzie Gets Married,' was shot as a test in front of a live studio audience with three cameras, leading the show to switch permanently to a three-camera live-audience format from season three onward.

Many exterior scenes for the show were actually filmed in Munster, Indiana, according to Ron Howard.

The season 5 episode 'Hollywood: Part 3,' in which Fonzie jumps over a shark on water skis, later inspired Jon Hein to coin the phrase 'jumping the shark' in 1985 to describe a show's decline, even though Happy Days remained the number-one program for years afterward.

In 2011, several original cast members, including Marion Ross, Don Most and Anson Williams, sued CBS for $10 million over unpaid merchandising revenues, a case reportedly triggered after Ross learned about a Happy Days-themed slot machine; the lawsuit was settled in 2012 with each actor receiving $65,000.

Robin Williams made his television debut as Mork in the 1978 episode 'My Favorite Orkan,' improvising much of his dialogue and physical comedy (including sitting on his head during the audition), which so impressed producers that he was signed to a contract within four days, leading to the spin-off Mork & Mindy.

The character Chuck Cunningham, Richie's older brother, mysteriously vanished from the show after season two without explanation, giving rise to the term 'Chuck Cunningham Syndrome' used to describe TV characters who disappear without narrative explanation.

The season one opening theme was a newly recorded version of 'Rock Around the Clock' by Bill Haley & His Comets, recorded in fall 1973 but not commercially released until 2005 by the German label Hydra Records.