Several thousand veterans, family members and others gathered at the Normandy American Cemetery and Memorial, with its 9,387 white marble tombstones on a bluff overlooking Omaha Beach, the emotional centerpiece of American pilgrimages to honor the men killed in Normandy.
For the ceremony, small U.S. and French flags were placed in the ground at each grave.
In addition to the fallen troops, Allied bombardments killed an estimated 20,000 French civilians, and Hollande paid tribute to them Friday in Caen, which like many cities of Normandy was largely destroyed in the bombings.
France has only tentatively come to grips with the invasion's toll on civilians. The Allied bombings — especially the deadly onslaught in Normandy during the invasion launched on D-Day — were used as a propaganda tool by the Vichy government, which collaborated with the Nazis. Historians now believe that nearly as many French civilians died in Allied air raids as Britons during the German Blitz.
Friday's commemorations also honored soldiers in today's conflicts.
Jeffrey McIllwain, professor at the San Diego State University school of public affairs, will lay a wreath on behalf of educators who have lost students to wars in Iraq and Afghanistan — himself included.
He wants to keep the memory of D-Day alive as the number of survivors dwindles, and brought 12 students to Normandy for a course on the lessons of D-Day.
"I make them promise to bring their grandchildren," he said, "to serve as a bridge to the next generation."
Echoing that message, children accompanied world leaders as they walked down a red carpet to enormous viewing stands for the main international ceremony Friday.
Veteran Jack Schlegel, 91, of Albany, New York, came to Normandy for the 40th, 50th and 60th anniversaries of D-Day, and says he's honored to be here for the 70th.
"The president of the VFW (Veterans of Foreign Wars) told me he wants to see me at the 75th but I don't know," said Schlegel, who was a paratrooper of the 82nd Airborne division. "My head's still here but I'm not sure about my body."
Julie Pace in Colleville-sur-Mer, and Angela Charlton in Paris, contributed to this report.