Former Atletico Madrid midfielder Costinha is delighted with his move to Atalanta.
The Portugal international completed his switch on Friday and said: "I had always dreamed of playing in Italy, so I am extremely happy with this transfer.
"I hope to do well for a club that has proved right away it intends to put its faith in me."
Costinha has signed a contract until June 30, 2010, but is not in the squad travelling to Calabria for Sunday afternoon's match with Reggina.
He could make his debut in Wednesday's Coppa Italia encounter at Ascoli.