The Gunners have brought in the talented defender, who can play at center half and left-back, from Bologna.
Having spent a mega sum on Calafiori, Edu knows that fans will be expecting a great deal from the team.
Sporting Director Edu said: “It has been a great team effort in completing this transfer and we welcome Riccardo to the family.
“We identified Riccardo as part of our strategy to sign players who fit our profile and will reinforce our squad to compete at the highest level. He is 22 but brings quality and experience. He will quickly grow into being an Arsenal player.
“Riccardo has consistently shown his quality for his club and country. He was one of the best players in Serie A last season, and gave strong performances for Italy in the Euros this summer. Mikel and our coaches are excited to start working with Riccardo, and we all look forward to seeing him in our shirt.”