After over 20 years of Santini producing the famous Maglia Rosa, the Giro d'Italia leaders' jerseys will be produced by another Italian brand from the 2018 season for at least four years.
Castelli will produce the famous maglia rosa for the general classification leader, maglia ciclamino for the points classification, maglia azzura for the king of the mountains, and the maglia bianca for the best placed young rider on the general classification.
Castelli has previously made the jerseys for the Giro d'Italia, with the last one worn by Miguel Indurain 25 years ago.
"We are really proud of having back the Scorpion on the roads of the Giro d'Italia," said Castelli's brand manager, Steve Smith. "For an Italian company being partner of RCS Sport in the toughest race in the world can only be a great joy. This is a great occasion to showcase an Italian company that's synonymous with excellence in cycling clothing."
Race organiser RCS added: "It's a real pleasure to announce the return of the prestigious international brand Castelli to the Giro d'Italia family. The historic company will once again produce the Giro leader's jerseys after our successful experience together in the 1980s and 1990s.
"We are certain that this will be an important and worthwhile partnership for both companies, for marketing and in terms of return on investment."
Last year, Castelli announced a three-year partnership with Team Sky, and it is no secret the British WorldTour team want to win the Italian Grand Tour in the future. Sky experienced bad luck at this year's race with a parked police motorbike taking down a group of GC favourites, including Geraint Thomas and Mikel Landa, in the first half of the race. While Thomas was subsequently forced to abandon, Landa would go on to win a stage and the mountains classification. Tom Dumoulin (Team Sunweb) won this year's Giro d'Italia, beating Nairo Quintana (Movistar) by 31 seconds.