The 27-year-old goalkeeper missed the entire 2011-12 campaign but the Rothosen believe that they have pulled off a major coup in landing the Germany international.
The goalkeeper, who missed all of last season through injury, has put pen to paper on a five-year contract with the Rothosen.
"If you can get a 27-year-old Germany international goalkeeper on a free transfer, then this is a special opportunity, which we have capitalized on," Hamburg sporting director Frank Arnesen enthused on the club's official website.
"I hope that by performing well with us, he can earn a recall to the national team."
Adler, for his part, is just looking forward to getting back on the field after his injury nightmare.
"I absolutely think that I will emerge stronger from the last year," he declared. "It was a tough time and I had many lows during my rehab, but in the end it has all paid off. I now feel fit and ready."
Alder, who has been capped 10 times by his country, was not included in Joachim Low's preliminary squad for Euro 2012.
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