Double Impact is a 1991 American action film written and directed by Sheldon Lettich, and written, produced by and starring Jean-Claude Van Damme as Chad and Alex Wagner. The film marks Van Damme's third collaboration with director Sheldon Lettich (who wrote Bloodsport and directed Lionheart) and second collaboration with Bolo Yeung (the first being Bloodsport in 1988). Double Impact was released in the United States on August 9, 1991.

In Hong Kong during the year 1966, business partners Paul Wagner and Nigel Griffith open the Victoria Harbour Tunnel. Paul attends with his wife Katherine and their identical twin infant sons, Chad and Alex. After the celebration, the family is followed home by their bodyguard, Frank Avery, whom they dismiss. Once he leaves, a Triad hit squad follows them. A shootout ensues, in which Paul is killed. Katherine begs the Triads to spare the twins but is killed by Moon, the top henchman. Their maid is able to escape with Alex and Frank eventually saves Chad; the maid leaves Alex at a Hong Kong orphanage and Frank raises Chad in France.

25 years later in 1991, Chad and Frank are running a successful martial arts dojo in Los Angeles when Frank tells a surprised Chad about a new "business" in Hong Kong. The two go to a mahjong parlor and a woman, mistaking Chad for Alex, takes him back to Alex's room. When Alex arrives, he knocks out Chad for being with his girlfriend, Danielle Wilde.

Frank tells them they are identical twin brothers and they need to join to take down Griffith and get their part of the royalties from the tunnel, but Chad and Alex initially do not get along with each other. Alex takes them out on his boat to sell smuggled Mercedes and cigarettes to some Chinese buyers, but the Hong Kong Police arrive and Chad dumps the cars to escape the cops faster. Back in Hong Kong, some thugs kidnap and beat up Chad (mistaking him for Alex) when he refuses to work for their leader, Raymond Zhang. Danielle, who works for Griffith, begins checking his private files for information, but she is being watched closely by Griffith's bodyguard, Kara.

Alex takes Chad and Frank to an abandoned hotel on an island to conduct their operations. With intelligence from Danielle, they attack a drug operation and blow it up. Next, they attack a club frequented by Zhang by pretending to bring him Cognac smuggled from France, which is actually just crates of bombs, although they fail to kill Zhang. Danielle continues to search for information but is caught and sexually molested by Kara. Danielle later calls the hideout revealing she has found something, but her phone is tapped by Griffith. Unable to find Alex and Frank who are out gathering firewood, Chad takes the boat to rescue Danielle by himself. However, Alex becomes paranoid and begins drinking heavily while imagining Chad and Danielle having sex. Chad brings Danielle home, but Kara follows them in a helicopter and discovers their hideout. When they return, Alex attacks Chad in a drunken rage before the brothers angrily part ways for the night.

The next morning Chad and Alex awaken to see Triads landing on the beach and, although they kill several, Frank and Danielle are captured. They capture one Triad who reveals that Frank and Danielle have been taken to Zhang's boat at a pier. Chad and Alex board and fight their way through the ship; Chad kills Moon (who beat him when he was kidnapped earlier) and he and Alex rescue Frank and Danielle. Afterwards, the twin brothers split up: Chad pursues Griffith and Alex chases Zhang. Alex eventually kills Zhang when he falls to his death from atop a crane. Chad and Danielle are chased through a maze of shipping containers until Griffith threatens to crush Chad with a forklift holding a container. Chad jumps into the water, sneaks around into the forklift, and drops the container on Griffith, killing him. Alex, Chad, Danielle and Frank reunite after the ordeal and appear to set aside their differences.

Van Damme was reportedly paid $600,000 for the movie. He hoped playing the dual role of Chad/Alex would change his image and help him break away from the martial arts movie genre he had become so popularly known for. "[Alex] is violent and [Chad] is not, so audiences [will] see the contrast in my work." Prior to the film's release, he had told the Los Angeles Times: "If I stay in martial arts pictures people will get tired of my films." Van Damme felt Double Impact's love scene would appeal to a wider audience. Seeing Jeremy Irons portray a dual role in Dead Ringers allegedly influenced Van Damme's decision.

Director Sheldon Lettich co-wrote the script with Van Damme. Inspiration was taken from Alexandre Dumas' The Corsican Brothers; an 1844 novella about twins separated at birth, who find each other in adulthood. Lettich later recalled the concept of Van Damme playing twins "was so successful that other producers wanted him to repeat it." (Timecop, Maximum Risk, Replicant) "Even though it meant a lot more work for Jean-Claude, he enjoyed the challenge of playing two distinctly different characters, showcasing a dark and a more light-hearted side in the same movie."