Boateng has been given Martin Petrov's old No 17 shirt after officially completing his £11million move to Manchester City.
Germany defender Boateng agreed a five-year deal and passed his medical at Eastlands last month and had to wait until day for the move to become official.
"I spoke at length with Roberto Mancini and he impressed me with his plans for the team in the coming seasons," he said. "It was a very good conversation.
"I know about City from when Hamburg played here in the UEFA Cup last year. I played in the second leg, which we lost, but we won the tie on aggregate on the way to the semi-finals."