It's a comedy film that's beloved of religious leaders, movies critics and audiences alike - and a movie whose title has become a phrase in its own right. A film that doesn't just provide laughs but questions about existentialism, too - and one that definitely bears repeated viewing. Appropriately enough.
So what better way to celebrate 2 February than to celebrate Harold Ramis's wonderful movie about that date - most notably its cracking screenplay by Ramis and Danny Rubin, and its brilliant performances from Bill Murray and the rest of the cast.
Here are 21 of the finest, funniest moments in a film that is made up of pretty much nothing but fine, funny moments. With a special mention to the one moment that never takes place: an explanation of why this is happening to Phil Connors in the first place. Because the absence of that moment is just one reason for the film's brilliance.
Take it away, Sonny and Cher...
The first time we hear 'I Got You Babe'
Of course, we don't realise how significant this song - and the DJs' chatter afterwards - is going to become. But it's instantly familiar, instantly a song you'd probably wake up to on the radio, probably one you'd find a bit annoying - and thus the perfect choice.
Phil meets Ned Ryerson
Bing! Stephen Tobolowsky may only have about five minutes of screen time in this film - but his character of Ned "the head" Ryerson is unforgettable. Am I right or am I right or am I right? Right right right?!
The first time the day is repeated
'I Got You Babe' comes on the radio, the DJs come out with the same patter, and Phil looks out of the window to see that there's been no blizzard. And instantly, we - and he - realise that something's wrong.
Phil gets drunk with two local guys
"What would you do if you were stuck in one place, and every day was exactly the same, and nothing that you did mattered?"
Phil punches Ned Ryerson in the face
And for the first time, steps over the icy puddle. (Fast forward to 3 minutes into this Ned compilation to enjoy it.)
Phil approaches a woman in the diner, asks her a few personal questions - and uses all the information to hit on her the next time he sees her. (Also great: Marita Geraghty's cute little 'right here' motion with her hands.)
"This is a man we're talking about, right?"
Rita describes her perfect guy. "He's intelligent, supportive, funny." "Me, me, me..." "He's romantic and courageous." "Me also..."
"I always drink to world peace."
In which Phil learns a little more every time he props up the bar with Rita.
The French literature scene
The first time, he laughs in her face. The second time? "You speak French?" "Oui."
The slaps montage
In which Phil fails to learn his lesson... over and over again.
Phil answers the questions on 'Jeopardy'
And in doing so, stuns the guests of the bed and breakfast he's staying in.
Phil smashes up the clock radio
A classic example of the screenwriting rule 'show, don't tell'.
Phil drives off with the groundhog
Thinking that Groundhog Day could end if there's no groundhog, Phil kidnaps Punxsutawney Phil... and the scene ends with a perfect line from Larry.
Phil introduces Rita to people in the diner
"You like boats, but not the ocean..." From Doris the waitress to Rita herself, Phil reveals what he knows about everyone in order to prove what's been happening to him.
Phil tells Rita she's "the kindest, sweetest, prettiest person I've ever met in my life".
And the best part? She responds with a drowsy "Did you say something?".
The piano teacher kicks out her pupil
Because Phil turns up on her doorstep offering $1,000 for a lesson.
Phil freaks out Ned Ryerson
With a homoerotic hug and the words "I don't know where you're headed - but can you call in sick?"
"Sometimes people just die." "Not today."
Previously, usually, he's passed him by. But when Phil finds the homeless man in an alleyway, he takes him to hospital - but he dies. On a later Groundhog Day, he tries to save his life... and fails.
Phil plays boogie woogie piano
Bill Murray. In shades. Playing boogie wooogie. And when he spots Rita, he starts playing Rachmaninov. Which he then swings.
Larry is sold at the bachelor auction
The Phil auction is great fun - but fast-forward to 1:40 to enjoy Chris Elliott's perfect awkward twirl... and Larry's horror at realising that the winning bid (25 cents) has been made by an elderly lady.
"Do you know what today is? Today is tomorrow."
(With a special mention for the line "I said stay, so you stayed? I can't even make a collie stay.") The spell is broken: 'I Got You Babe' plays - but the DJs don't say "OK campers, rise and shine!" - and Rita's arm reaches across to hit the snooze button. Perfect.