Huge crowds and some 40 world leaders are taking part in a unity march in Paris after 17 people were killed during three days of deadly attacks.
More than a million are expected to march through the streets.
"Paris is the capital of the world today," French leader Francois Hollande said. "The whole country will rise up."
The marchers hope to demonstrate unity after the attacks on satirical magazine Charlie Hebdo, police officers, and a supermarket.
Ahead of the rally, a video emerged appearing to show the supermarket attacker, Amedy Coulibaly, pledging allegiance to the so-called Islamic State.
In the video, he said he was working with the Charlie Hebdo attackers: "We have split our team into two... to increase the impact of our actions."
Leaders link arms
Sunday's Paris rally is expected to be even bigger than the combined total turnout for marches across France on Saturday, when 700,000 people took to the streets to remember the victims.
The march, led by relatives of the victims of last week's attacks, left Place de la Republique.
The British, German, Turkish, Jordanian, Israeli and Palestinian leaders are among the world leaders taking part in the rally.
World leaders observed a minute's silence, and linked arms in an act of solidarity as the march began.
About 2,000 police officers and 1,350 soldiers - including elite marksmen on rooftops - have been deployed to protect participants.
The march has been split into two routes for security purposes. Both rallies began at the Place de la Republique and finish at the Place de la Nation.
Marchers in Paris chanted "liberte" ("freedom") and "Charlie" in reference to the Charlie Hebdo magazine.
Some waved French flags, cheered, and sang the national anthem. A group of demonstrators carried a large model pencil with the words "not afraid" written on the side.
In Marseille, in the south of the country, thousands also marched against the attacks.
Samia Ghali, mayor of one of the city's districts, told the BBC that people were marching for tolerance and co-existence. Marseille is the city with the largest Muslim population in France.