Bobby Wood has joined Hamburg from Union Berlin on a four-year contract.
Wood, 23, scored 17 goals in 30 matches in Germany's second tier.
Wood has a place on the United States' 40-man preliminary squad for the Copa America.
Wood said on Union Berlin's official website: "I can only thank everyone here for the support this year. At Union, I got a lot of trust and won a lot of minutes. I was able to make the next step here and also to win the confidence you need as a forward to score goals. It makes me proud that I have become a part of the club's history with my goals."