Diamond Is Unbreakable (Japanese: ダイヤモンドは砕けない, Hepburn: Daiyamondo wa Kudakenai; sometimes translated as Diamond Is Not Crash) is the fourth main story arc of the Japanese manga series JoJo's Bizarre Adventure, written and illustrated by Hirohiko Araki. It was serialized in Shueisha's Weekly Shōnen Jump for a little more than 3+1⁄2 years, from May 4, 1992, to December 4, 1995, with the 174 chapters collected into eighteen tankōbon volumes. In its original publication, it was titled JoJo's Bizarre Adventure Part 4: Jōsuke Higashikata (ジョジョの奇妙な冒険 第4部 東方仗助, JoJo no Kimyō na Bōken Dai Yon Bu: Higashikata Jōsuke). It was preceded by Stardust Crusaders and followed by Golden Wind.

This part introduces the Stand Arrow, which causes anyone pierced by it to develop a Stand if they are mentally strong enough. The Arrow was retroactively revealed to be the source of Dio's stand as well as the Joestar family's stands. The arc was adapted into an anime television series by David Production, JoJo's Bizarre Adventure: Diamond Is Unbreakable, that began in April 2016. A live-action film adaptation by Toho and Warner Bros. titled JoJo's Bizarre Adventure: Diamond Is Unbreakable Chapter I was released on August 4, 2017. Viz Media released the manga in English in a nine-volume compiled format from 2019 to 2021.

In 1999, Jotaro Kujo arrives to the town of Morioh (杜王町, Moriō-chō) in the M-Prefecture (M県, Emu-ken) after learning that his grandfather Joseph Joestar has an illegitimate son while compiling a list of beneficiaries. He bumps into a freshman named Koichi Hirose before the two encounter the youth Jotaro is looking for: A highschool student named Josuke Higashikata, whose Stand Crazy Diamond allows him to manipulate matter in ways that include repairing and healing. Fighting Josuke after inadvertently insulting his pompadour, Jotaro explains the nature of Stands and that one is being used by a death row inmate named Anjuro "Angelo" Katagiri, who escaped to Morioh. Josuke unknowingly makes an enemy of Angelo, who murders his grandfather before Josuke uses his power to fuse Angelo into a rock. However, Angelo uses his final moments of consciousness to reveal someone hit him with an Arrow that gave him his Stand, Jotaro learning that an actual artifact was possessed by Dio's forces. Josuke and Koichi eventually come across the culprit, Keicho Nijimura, who inflicts Koichi with the Arrow while his younger brother Okuyasu holds Josuke off. Josuke defeats Okuyasu and heals Koichi with Crazy Diamond, with Koichi developing a Stand called Echoes. After Keicho is defeated with his reason of creating Stand users to create someone able to mercy kill his father, a mutated subordinate of Dio's, Keicho is killed by Stand Red Hot Chili Pepper, which takes the Bow and Arrow. Okuyasu then joins Josuke's group to avenge his brother, encountering several other Stand users Keicho created before they eventually find and defeat Akira Otoishi, Red Hot Chili Pepper's user, as Joseph arrives in Morioh. The Bow and Arrow are taken into Jotaro's custody and all seems to be over for the moment.

Soon afterward, after Josuke tries spending time with Joseph as they find a baby with an invisibility stand, the group encounters other Stand users such as eccentric manga artist Rohan Kishibe, middle schooler Shigekiyo "Shigechi" Yangu, and a beautician named Aya Tsuji. Koichi and Rohan later meet the ghosts of Reimi Sugimoto and her dog Arnold after stumbling into the mysterious Ghost Alley, learning of a serial killer who has been lurking in Morioh for years. The murderer is a handsome office worker named Yoshikage Kira, who seeks to satisfy his murderous hand fetish obsession while living a peaceful, quiet life by using the destructive ability of his Stand, Killer Queen, to erase any evidence of his crimes. But his prompted murder of Shigechi ends up exposing him during a brief battle with Jotaro and Koichi that left him injured as Josuke and Okuyasu arrive. Kira escapes and forces Aya to use her Stand to swap identities with a man Kosaku Kawajiri, killing them both while assuming Kosaku's life. Kira's father Yoshihiro, a ghost who uses his Stand to live on in a photo, uses a Bow and Arrow he received years ago from Enya Geil to create an army of Stand users to protect his son, including a dying cat that reincarnated as a Stand-plant hybrid named Stray Cat which Kira took as a pet.

Kosaku's son Hayato Kawajiri begins to suspect his father's imposter and confronts Kira, only to get murdered with Kira panicking before receiving a new ability after pierced by Yoshihiro's Arrow a second time that allows him to revive Hayato. The following morning, Hayato learns Kira inflicted him with Killer Queen's new ability Bites the Dust, which destroys whoever Hayato reveals Kira's identity to while rewinding time back an hour with the victim's fate fixed. After Rohan died in one loop and Josuke's group the next, Hayato realizes he needs to force Kira into canceling Bites the Dust before the others are killed with their deaths made permanent. Hayato exploits the knowledge he gained from the time loop to wake Josuke up early and arrange for him to overhear Kira blowing his cover. Kira is forced to use Killer Queen to defend himself, which cancels Bites the Dust just in time to save Josuke and his allies.

Josuke engages Kira in a pitched battle, Okuyasu seemingly killed as Josuke and Hayato take refuge in a house when Kira combines his Stand's powers with Stray Cat to create invisible projectile bombs. Kira plants Yoshihiro's photo into Hayato's pocket to track Josuke, only to be tricked into destroying his father before Okuyasu appears in the nick of time to swipe Stray Cat and further disadvantage Kira. As Jotaro, Koichi, and Rohan arrive with emergency workers responding to the explosions, Kira attempts to activate Bites the Dust on a nearby paramedic in a last ditch attempt to avert his defeat. But he is stopped by Jotaro with assistance from Koichi, knocked into the path of an arriving ambulance that accidentally crushes his skull. Kira's ghost ends up in Ghost Alley and is confronted by Reimi, who gets him dragged off into an unknown fate by spectral hands. Her mission accomplished, Reimi gives the group her final farewells and moves on to the afterlife. The next day, Josuke bids farewell to Jotaro and Joseph, who leave Morioh as the summer of 1999 draws to a close.

Diamond Is Unbreakable is set in the fictional town of Morioh located in S-City, M-Prefecture, which is modeled after a specific area in Hirohiko Araki's hometown of Sendai, Miyagi Prefecture. The author said that the suspense and fear caused by the "unusual" and "mysterious" residents there were his inspiration. Although he originally intended for JoJo's Bizarre Adventure to be a "mythical" manga with superpowers and such, he enjoyed drawing the "feeling of everyday life" in Diamond Is Unbreakable. Because he wanted to create a "closed city," the Stands featured were not proactively attacking.

During Diamond Is Unbreakable's serialization, Araki received feedback from readers who felt that enemies in the manga had gotten weak. Although he usually does not respond to reader opinions, he had heard similar comments from the editorial team and so made an exception by stating that "the weaknesses inside the hearts of people" are a thematic element of Part 4. He explained that sometimes he has a character's inner weaknesses drive them into a desperate situation, while other times he turns the weakness into something "dreadful" and bases a Stand off of it. Araki wrote that constantly having stronger and stronger enemies appear in a manga eventually leads you to "trying to think of the farthest edges of the universe", but in the real world, "true strength is found in not doing bad things. An enemy who does bad things is a person with an inner weakness."