The 22-year-old, who spent last season on loan at Brescia, impressed at the European Under-21 Championships in Israel as Italy finished runners-up to Spain.
"Luca Caldirola is a very interesting player," said Bremen's director of sport Thomas Eichin.
"In spite of his young age he has plenty of experience. He is captain of Italy's Under-21s and has proven his leadership qualities at his previous clubs.
"We saw at the Under-21 Championships that he has lots of potential. He has a fine technique and a good eye, and he is very creative in opening up play too.
"We are delighted he has opted for Werder."
Caldirola, who passed his medical today, is looking forward to meeting his new team-mates.
"Werder Bremen is a big chance for me," he said. "As soon as my agent told me of Bremen's interest, I said I wanted to join them straight away.
"They're a club with a great tradition and I'm looking forward to the coming years."
Eichin has also dismissed reports linking Bundesliga side Bremen to numerous players, although links with former Borussia Dortmund striker Lucas Barrios were too strong for the director of sport to deny.
"I am regularly offered the services of up to 80 players every day.
"I am more than carefully looking at a name like (Lucas) Barrios, talking to my scouts and my manager about it.
"Of course, we will definitely keep on talking about this."
Barrios hopes to be available on a free transfer following contract wranglings with current club Guangzhou Evergrande of the Chinese Super League. The Paraguay international claims that he hasn't been paid by the club, having signed a four-year deal in July 2012.