Once a year, a select group of New Yorkers shed their stereotypical all-black ensembles and dress head-to-toe in white to gather for a picnic. But this isn't your average evening dining al fresco — instead it's a secretive yet over-the-top spectacle even Jay Gatsby would approve of. This is Le Diner en Blanc. New York City's eighth annual Le Diner en Blanc is scheduled to take place Monday. On the day of the dinner, 6,500 party-goers dressed in elaborate, all-white ensembles will gather at 30 predetermined locations scattered throughout the city, carrying their picnic baskets and lugging their own folding tables, chairs and tablecloths. They'll then be shepherded en masse by volunteers to the 2018 dinner's secret location (for the past seven years it's been in Manhattan). There they'll set up their spread and eat, drink and dance the night away.

Le Diner en Blanc New York City, 2016. Source: Jane Kratochvil

Though the party is relatively new to New York, the city's picnic now has a 45,000-person waiting list. But the concept for the event originated in France in the 1980s and has since spread to cities across the globe.

Le Diner en Blanc in New York City, 2017 Source: Eric Vitale Photography

"My business partner's dad in 1988, 30 years ago, created the concept in France by accident," Sandy Safi, co-founder of Le Diner en Blanc International based in Montreal, tells CNBC Make It. "Their backyard was too small, so they decided to go to a park; they were returning from holiday and they wanted to see friends and friends of friends. "So they said, 'Come to the park and dress in all white so we recognize everybody that's part of the group. Bring tables and chairs and let's go have a picnic,'" she explains. "It kind of grew from there. That was the grandfather of all pop-ups."

Le Diner en Blanc in Las Vegas, 2018 Source: Tony Tran

Now, Le Diner en Blanc draws 120,000 participants worldwide; the parties are held on six different continents in 30 countries across 80 cities, including far-flung locations like Havana, Cuba and Madrid, Spain. The event celebrated its 30th anniversary in Paris, France in June, drawing a record 17,000 participants.

Le Diner en Blanc in Panama, 2018 Source: Nicolas Droz

So how do you get an invite to the "world's largest dinner party," as its been dubbed? Invites (priced at $43 per person for New York City's event) are issued to people in phases: Phase 1 invitees are those who attended the dinner the previous year and Phase 2 are people referred by Phase 1 attendees. It's not until Phase 3 when a limited number of invites are released to those on the lengthy waiting list (which can you sign up for here). While it varies country to country and city to city, Phase 1 typically opens around four to six weeks before the event, while Phases 2 and Phase 3 are spaced just a few days apart. Each person is required to purchase two tickets; no more or no less. Once your participation is confirmed, you must attend, rain or shine, or risk losing your spot on next year's guest list. (This reporter went in 2016, when roughly 5,000 people flocked to the pop-up picnic's location in Battery Park, but skipped the 2017 at Lincoln Center and was not invited back for 2018.) If you want to be invited back there are many other rules you must follow as well. The dress code is described as "elegant and white only," (according to my 2016 invitation that means no ivory, cream or eggshell and the only accepted splashes of color are silver and gold for accessories). Originality is encouraged "as long as it is stylish and tasteful," (no baseball caps, t-shirts, tank-tops, sport shoes or flip flops, says my old invite).

Le Diner en Blanc in New York City, 2017 Source: Eric Vitale Photography

Guests are required to bring table settings (they must be all white), a folding table, a total of two white chairs and a white tablecloth.

Le Diner en Blanc in Paris, 2018. Source: Fabrice Malard

You can either bring your own picnic basket or pre-order one during registration (available for pick-up once on site). BYO picnic baskets must include fine food, proper stemware and white dinnerware (meaning plates and such, but silverware is fine. Le Diner en Blanc says there is no disposable dinnerware used during its event). As for the catered baskets, this year, N.Y.C. will have renowned chef and Michelin star recipient Marc Forgione curating four picnic baskets. There is no beer or hard liquor allowed, but you can purchase wine through the event, priced at $30 to $50 a bottle, and champagne for $55 (though no more than two per table allowed).

Le Diner en Blanc Philadelphia, 2017. Source: Georgi Anastasov Photography

Guests must meet at their assigned locations throughout the city and then walk or take public transit to the final destination.

Guests attending Le Diner en Blanc in New York City, 2017. Source: Hal Horowtiz

"All of those are rules for eligibility," says Safi. "If you show up to a gathering point dressed in another color, you won't be allowed to move forward." The rigid rules add to the event's allure, she says. "Just planning the ultimate picnic and bringing it with you and meeting at a gathering point, dressing in white from head to toe, playing the game..." Safi says. "I think it brings together people from all different demographics that have a love for everything that's a sharing experience — outdoor events, foodies, a bit of fashion — and I think it's the participatory nature of the event," Safi explains. "It's very unique as opposed to any other kind of event where you just show up and you don't have to really do anything other than attend. Here, each one of the participants is making the event for themselves, as well as for other people with everything they do, with their tables and chairs and decorations, their outfits," she adds. "I think that participation is really what is unique about this event….it creates a certain kind of unity and energy."

Le Diner en Blanc in New York City, 2016. Source: Eric Vitale Photography