The main protagonist is a 37 year-old woman named Loretta Castorini (Cher). The first scene - in a funeral parlor where she prepares an income tax report and sharply reproves the owner for the mess in his receipts and documents - instantly defines her character: a cool and rational woman, dressed in neat, sober clothing, who makes and executes carefully-detailed plans in both her personal and professional life, and who habitually manages the life of men.
Especially, she manages the life of the 42-year old Johnny Cammareri (Danny Aiello) who rather clumsily proposes to her in the early part of the film (with her immediately taking charge of the process and instructing him in the details of how to carry on).
The main theme of the film is the process by which Loretta is suddenly caught up and swept off her feet (literally, in one scene) by an overwhelming passionate love, defying all her plans and preparations - a passionate love which is explicitly compared with that of the protagonists in Puccini's "La Boheme", the difference being that this is a romantic comedy and not a Puccini opera (and therefore, the ending is bound to be different than that of the opera).
There are numerous sub-plots woven throughout the film, mostly involving the older members of Loretta's family - who live in a single, enormous house in Brooklyn: Loretta's parents, who had married for love but whose marriage is undergoing a deep crisis due to the father's infidelity, and Loretta's paternal grandfather, who always walks the streets with his numerous dogs, sees and knows everything and usually keeps his silence. In addition, there is an uncle and aunt who, on the contrary, undergo a kind of "second honeymoon"; and Loretta's mother meets and shares a meal with an aging professor (virtually the only non-Italian in the film) who keeps having short affairs with his female students, which invariably start with the girl being fascinated and end with her throwing a drink in his face and walking away.
The main plot starts with Johnny who, after proposing to Loretta, must visit his dying mother in Palermo, Italy before their marriage. He leaves her to make all preparations ("I will take care of everything, you just have to show up"). Loretta's father, Cosmo (Vincent Gardenia) does not approve of the marriage because he believes Loretta has bad luck in marriage (which she herself had stated to Johnny) and because Johnny is a "mama's boy". Loretta had been married once already. Her first husband died when he was hit by a bus. Her mother, Rose (Olympia Dukakis), does not really care about the marriage, but her question is:
Rose: "Do you love him?" Loretta: "No, Ma." Rose: "Good. 'Cause when you love 'em, they drive you crazy, because they know they can. But you like him?" Loretta: "Oh yeah. He's a sweet man, Ma."
Johnny says that he wants her to talk his younger brother, Ronny (Nicolas Cage) into coming to the wedding; this request is reiterated once Johnny reaches Italy and calls Loretta from Palermo. He also warns her that there has been some "bad blood" between the two. She then visits Ronny and finds out that Ronny lost his hand, and consequently his fiancée, while slicing bread for his brother, Johnny. While this "bad blood" makes no sense to Loretta, she is taken by Ronny's passionate and poetic ways and offers to make him something to eat. During that time Loretta makes it clear to Ronny that she thinks the grudge he holds is stupid. Their mutual attraction then takes over and they make love. They wake up later and Loretta feels ashamed of herself. She says she could never see Ronny again and they must never tell anyone what they did, but Ronny is instantly hooked and Loretta too in her own way.
After feeling bad for betraying her fiance, Loretta goes to church and sees her mother Rose praying. Rose indicates to Loretta that Cosmo might be cheating on her. Ronny decides to woo Loretta by taking her to the opera later that day. Loretta dyes her hair and gets a beautiful dress. At the opera, both Loretta and her father Cosmo catch each other being unfaithful. Cosmo says "You are my daughter. I will not have you acting like a puttana (Italian for whore)." But Loretta responds "And you are my father..." They both decide to go their separate ways and pretend they saw nothing. Walking home, Loretta feels guilty for her actions but Ronny convinces her, in so many words, that there should be no regrets and they should follow their hearts.
Later that night at the Castorini house, Johnny arrives back from Palermo. His mother has made a miraculous recovery and he has something important to tell Loretta. Loretta shows up the next morning with love bites on her neck and is shocked that Johnny has returned. Ronny arrives at the house to confront his brother with the fact that he is in love with Loretta. At the same time, Rose confronts Cosmo about his affair, and he agrees to stop seeing his girlfriend. Johnny shocks the whole family by telling Loretta that he can't marry her. Even though upset, Loretta is relieved because that was the opportunity for Ronny to prove his love to Loretta and everyone else by proposing.
Rose: "Do you love him, Loretta?" Loretta: "Ma, I love him awful." Rose: "Oh, God, that's too bad."
Loretta accepts Ronny's proposal and the whole family toasts "Alla famiglia!" (To the family!).
In June 2008, AFI revealed its "Ten top Ten"—the best ten films in ten "classic" American film genres—after polling over 1,500 people from the creative community. Moonstruck was acknowledged as the eighth best film in the romantic comedy genre. The film is also number 72 on Bravo's "100 Funniest Movies," and number 41 on AFI's 100 Years... 100 Laughs.