This year's Nobel Peace Prize has been awarded jointly to three women - Liberian President Ellen Johnson Sirleaf, Liberian Leymah Gbowee and Tawakul Karman of Yemen.
They were recognised for their "non-violent struggle for the safety of women and for women's rights to full participation in peace-building work".
Mrs Sirleaf is Africa's first female elected head of state, Ms Gbowee is a Liberian peace activist and Ms Karman is a leading figure in Yemen's pro-democracy movement.
"We cannot achieve democracy and lasting peace in the world unless women achieve the same opportunities as men to influence developments at all levels of society," said Nobel Committee chairman Thorbjorn Jagland in Oslo.
Reading from the prize citation, he said the committee hoped the prize would "help to bring an end to the suppression of women that still occurs in many countries, and to realise the great potential for democracy and peace that women can represent".
German Chancellor Angela Merkel - deemed by Forbes the world's most powerful woman - called the award a "wise decision".
But Mrs Sirleaf's main rival in polls this coming Tuesday, Winston Tubman, told the BBC she did not deserve the prize and was a "warmonger".
Mrs Karman heard of her win from protest camp Change Square in the capital Sanaa, where she has been living for several months calling for President Ali Abdullah Saleh to stand down.
She was recognised for playing a leading part in the struggle for women's rights in Yemen's pro-democracy protests "in the most trying circumstances" and is the first Arab woman to win the prize.
As the head of Yemeni organisation Women Journalists without Chains, Mrs Karman has been jailed several times.
Mrs Karman told BBC Arabic she was dedicating it to "all the martyrs and wounded of the Arab Spring" - the wave of unrest which has swept the Middle East and North Africa in the past year - and to "all the free people who are fighting for their rights".
Mr Jagland said the oppression of women was "the most important issue" in the Arab world and that awarding the prize to Ms Karman was "giving the signal that if it [the Arab Spring] is to succeed with efforts to make democracy, it has to include women".
Mrs Sirleaf, 72, who had been widely tipped as a winner, said the award was "for all Liberian people" and a recognition of "many years of struggle for justice".
She was elected in 2005, following the end of Liberia's bloody and ruinous 14-year civil war.
Upon coming to office, the US-educated economist and former finance minister - known as Liberia's "Iron Lady" - pledged to fight corruption and bring "motherly sensitivity and emotion to the presidency".
Mrs Sirleaf is standing in Tuesday's election, having previously said she would only hold the presidency for one term.
Her rival Mr Tubman denounced the award, saying she had "brought war here".
She had initially backed the rebels of Charles Taylor - currently on trial for war crimes in The Hague.
Although she has apologised, Liberia's Truth and Reconciliation Commission recommended that she be barred from holding public office for 30 years.
"I did more to stop the war than she did because she was for continuing the war," Mr Tubman said.
"Now that the war has stopped she wants to continue on top of the country as though she is some liberator. She is not."
He told AFP news agency the timing of the award was "provocative".
But Archbishop Desmond Tutu and U2 singer Bono welcomed Mrs Sirleaf's honouring, with Mr Tutu telling AFP: "Woo hoo. She deserves it many times over. She's brought stability to a place that was going to hell."
Her compatriot Ms Gbowee was a leading critic of the violence during the Liberian civil war, mobilising women across ethnic and religious lines in peace activism and encouraging them to participate in elections.
In 2003 she led a march through the capital, Monrovia, demanding an end to the rape of women by soldiers.
The Nobel Committee said she had "worked to enhance the influence of women in West Africa during and after war".
Ms Gbowee told the BBC's Focus on Africa programme: "I am confused. I am humbled. This is the first time in the 39 years of my life that I am out of words.
"This is a victory for women rights everywhere in the world. What could be better then three women winning the prize?
"This is the recognition that we hear you, we see you, we acknowledge you."
The women will share the $1.5m (£1m) prize money.
The BBC's world affairs correspondent Mike Wooldridge says that the Nobel Peace Prize originally recognised those who had already achieved peace, but that its scope has broadened in recent years to encourage those working towards peace and acknowledge work in progress.
The Nobel committee received a record 241 nominations for this year's prize - among the individuals and groups believed to have been put forward were the European Union, Facebook founder Mark Zuckerberg and key cyber dissidents in the Arab Spring movement.