The Duchess of Cornwall will join Jamie Oliver to launch what could be the biggest community event since the Queen's Diamond Jubilee in the wake of the murder of MP Jo Cox.
The Great Get Together, which will involve tens of thousands of community get-togethers on the weekend of June 17 and 18, has been put together by The Jo Cox Foundation and The Big Lunch along with dozens of other community groups.
Mrs Cox was killed outside her constituency office in Birstall, West Yorkshire, on June 16 last year.
The event is designed to bring people together within communities and Mrs Cox's widower, Brendan, said there could be "no more fitting tribute" to his wife than an event with this aim.
He said: "Jo loved a party and she would have been thrilled by the idea of The Great Get Together.
"As she said in her maiden speech in parliament - we have far more in common than that which divides us.
"Jo wanted a chance to bring our communities together to celebrate what unites us.
"There could be no more fitting tribute to her memory than The Great Get Together helping to do just that."
People are being invited to come together with friends, neighbours and strangers for street parties, picnics, barbecues and bake-off competitions.
Organisers say they expect it to be the biggest event of its kind since the jubilee celebrations in 2012.
Further details will be announced at a launch hosted by Camilla, who is patron of The Big Lunch, at Clarence House, in central London, on Wednesday.
The Duchess will be joined in the kitchen by Jamie Oliver and Mr Cox will also speak.
Jamie Oliver said: "There's nothing better than a good get-together with friends, family and amazing food.
"The Great Get Together takes it to a whole new level.
"Food connects us to the best things in life - it breaks down barriers, and gets people talking and sharing happy times like nothing else.
"This is an awesome initiative, and I'm really proud to add my support."
Peter Stewart, of The Big Lunch, said: "The Great Get Together will be a fantastic celebration.
"The Big Lunch is all about sharing food and coming together with your neighbours.
"In 2012, 8.5 million people took part in The Big Jubilee Lunch in parks, streets, gardens and community spaces, all having a great time together.
"Like Jo, we believe in togetherness and achieving a sense of community, collaboration and fun. We want to share that idea with everyone."
The Big Lunch was started in 2009 by the Eden Project and is funded by the Big Lottery Fund.