European leaders attended Thursday's ceremony at Krakow Cathedral
Poland is marking the 20th anniversary of the elections that led to the formation of the first non-communist government in the former Soviet bloc.
Ceremonies began with a service at Krakow cathedral attended by PM Donald Tusk and the former leader of the Solidarity union movement, Lech Walesa.
In 1989, Solidarity won an overwhelming victory in the first, partially-free elections in communist Eastern Europe.
The vote paved the way for the gradual end of communist rule in the region.
In December the following year, Mr Walesa was swept to power Poland's first democratically elected president.
'It started in Poland'
European leaders including German Chancellor Angela Merkel, Ukrainian Prime Minister Yulia Tymoshenko, and the former Czech President, Vaclav Havel, attended the ceremony at Krakow Cathedral on Thursday marking the election that heralded the collapse of communism.
The Polish model served as an example for next countries and in this way it might have speeded up peaceful transition to a better system based on democracy
Leszek Balcerowicz, Minister in first Solidarity government
The BBC's Adam Easton in Krakow says Poland is a deeply religious country, and the Polish Catholic Church and Pope, John Paul II, played an important role supporting the Solidarity movement in its struggle for democracy.
With hindsight it seems obvious, but at the time Solidarity's victory surprised almost everyone, our correspondent says.
Just six weeks before polling day the organisation was still banned.
It had survived underground despite the communist authorities' attempts to crush it by imposing martial law in 1981.
By 1989, the Polish economy was facing collapse and the former Soviet Union under Mikhail Gorbachev had signalled it would no longer intervene in Eastern Europe.
The Communist Party began talks with Solidarity and agreed to hold elections as a calculated concession to allow it a limited platform. They thought the opposition was too weak to organise, let alone win them, our correspondent says.
Poland's first post-war election propelled Solidarity into government
Solidarity's victory - the movement won 99 out of 100 seats in the newly created Senate and every seat available to it in the lower house, the Sejm - caught many by surprise and communism collapsed in Poland without bloodshed, he adds.
Leszek Balcerowicz, a minister in the first Solidarity government, told the BBC that it was an example for the rest of the region.
"The Polish model served as an example for next countries and in this way it might have speeded up the peaceful transition from a bad system to a better system based on democracy, market economy and civil society," he said.
One banner outside Krakow's cathedral on Thursday read: "1989, it all started in Poland".
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