April 30 was designated International Jazz day by UNESCO last year, but the first celebration will begin on Friday, with a Paris masterclass at the oddly early hour for jazzmen of 10.00 am to be followed by a Hancock gig in the evening.
On Monday, Hancock, Diane Reeves, Terence Blanchard, Ellis Wynton Marsalis will play as the sun comes up over Congo Square in the Big Easy, before the main event that night at UN Headquarters in New York.
There, Hancock will be joined by musicians from five continents, including Dee Dee Bridgewater, Diane Reeves, Romero Lubamo, Esperanza Spalding, Angelique Kidjo and Zakir Hussain for a concert broadcast globally.
Although the United States cut off funding for UNESCO over its recognition of Palestine, the agency will celebrate this most American artform as a force for "peace, unity, dialogue and enhanced cooperation among people."
"I believe that it is very important for young people to learn about music in all of its rich and varied aspects," said singer Barbara Hendricks, who will take part in the Paris opening party.
"It is very clear that when you hear music from Africa, from Mali, Senegal Nigeria, or you listen to delta blues from Mississippi, they're speaking the same language," she said.
"So all we have to do is to play more together, listen to each other play, play for others, and let that conversation continue to happen."
UNESCO's 1,200-seat concert hall in Paris has been fully booked for weeks, with fans keen to catch Hancock playing with legends like South Africa's Hugh Masekela and singers Hendricks and Tania Maria.
Hendricks began her career as a classical opera singer, but wants young people to follow her into jazz, which she she says forms part of "humanity's cultural heritage".