Germany has been marking 15 years since reunification at a time of great political uncertainty and continuing east-west divisions.
Many Germans still have mixed feelings about reunification
President Horst Koehler and Chancellor Gerhard Schroeder were joined by Mikhail Gorbachev at ceremonies in the city of Potsdam, outside Berlin.
East and West Germany were reunified in 1990 after the fall of the Berlin Wall.
Despite people's hopes at the time, living standards in the East have remained below those in the West.
But Brandenburg state premier Matthias Platzeck, the host of the national Unity Day ceremony in Potsdam, told invited guests: "We must succeed in overcoming the despondency and navel-gazing.
"We should grasp all of the spirit and emotion and power that all Germans felt inside themselves in 1989 and 1990 and commit to the future of Germany."
Chancellor Schroeder and Mr Gorbachev, the former Soviet leader, were to plant a cherry tree in Potsdam to mark the anniversary.
Parliamentary speaker Wolfgang Thierse, a former East German dissident, said Germans must rediscover the courage and sense of community needed to meet the still daunting challenges of reunification.
"We have ever more beacons, centres of growth and regions that are clearly on the path to success," AFP quoted him as saying.
"We have made significant progress, despite all the economic and social differences in the country."
The BBC's Berlin correspondent Ray Furlong says the recent indecisive elections show that although the Berlin Wall is long gone, divisions remain in people's minds.
The Christian Democrats (CDU), for instance, scored 37% support in West Germany but just 25% in the East. The new left party Die Linke, by contrast, won just 4.9% support in the West - but 25% in the East.
Germans had high hopes for the future in October 1990
Our correspondent says it is a reflection of the fact that living standards in the East are still much lower.
Unemployment there is almost twice as high, and the population has fallen by 900,000 as people have moved West in search of opportunities. Last year, the population fell by a further 50,000.
The German government insists progress is being made - net incomes have doubled in the last 15 years, now reaching 85% of Western levels - but admits great challenges remain.
Our correspondent says that since reunification a trillion euros has been transferred from West to East, to boost the economy there. The government foresees a further 150 billion euros in subsidies until the year 2019.