Barack Obama's plane, bearing the slogan "Change we can believe in", arrived in Berlin from Israel.
Climate change activists turned out in the city for the US presidential hopeful's much-anticipated visit.
Mr Obama met German Chancellor Angela Merkel at her office opposite the Reichstag.
Enthusiastic supporters cheered Mr Obama's motorcade as it passed through the German capital.
Mr Obama worked out at his hotel during the day and could be seen in a T-shirt in his car .
One John McCain supporter seemed determined to remind Berliners there will be more than one contender in November's election.
In Berlin's Tiergarten, thousands of people waited patiently to hear Mr Obama speak on foreign policy issues.
Correspondents spoke of a festive atmosphere more akin to a rock concert than a political speech.
Many only caught a glimpse of the US Senator, who spoke from a platform in the centre of the packed park.
Mr Obama arrived on stage to rapturous applause, to deliver a wide-ranging speech in which he called for America's partnership with Europe to be renewed.