The former Inter Primavera centre-half, who skippered the Azzurrini in the European Championship, has put pen to paper on a three-year contract with the Bundesliga side
The Italy Under-21 international signed a four-year contract with the German outfit and is already looking forward to his first taste of Bundesliga football.
"Bremen is a great opportunity for me," Caldirola is quoted as saying by his new club's official website.
"When my agent told me about the interest of the club I immediately said that I would love to play in Bremen.
"It is a club of great tradition and I cannot wait to start."
Bremen's sporting director, Thomas Eichin, is in no doubt that the 22-year-old centre-half will prove a great success at the Weserstadion.
"Caldirola is such an interesting player and, despite his young age, already has a lot of experience.
"He is the captain of the Italy U21s and he has also shown great leadership with the clubs that he has previously represented.
"He's very good at opening the game up, has great vision and we are delighted that he has chosen Werder."
Caldirola, who has represented his country at every under-age level, came through the youth team ranks at Inter before being the subject of a co-ownership deal with Cesena.