The World's Big Sleep Out 2019 will take place at locations around the world - including Edinburgh - and it's being backed by celebrities like Will Smith and Helen Mirren.
Partners for the campaign, Social Bite, Malala Fund, UNICEF USA and the Institute of Global Homelessness, aim to raise $50 million through this year's campaign to tackle homelessness.
Registration closes on Wednesday 4 December, so here's how to get involved and what you need to know before you sleep out.
What is The World's Big Sleep Out?
The World's Big Sleep Out trust was established by Social Bite’s Co-Founder Josh Littlejohn to take the Sleep in the Park concept worldwide.
Social Bite started out in 2012 as a sandwich shop in Edinburgh, offering employment and food for those without homes, with all of the profits going to charitable causes.
The charity has since grown to operate five stores across Scotland, and has organised a number of successful Sleep Out events, with 300 people taking part in the first one in Edinburgh in 2016.
Since then the event has grown in popularity, with 8,000 people taking part in the 2017 event and 10,000 people taking part in 2018 at cities throughout Scotland.
What was born in Scotland is now being taken to the global stage.
Where is this year's Big Sleep Out taking place?
This December, The World's Big Sleep Out will see 50 cities and towns across the planet join forces to take on homelessness, with Will Smith, Dame Helen Mirren and some big-name musicians getting involved.
Over 50,000 people are expected to take part, with the goal of raising $50 million.
Sleep Outs have been planned in cities across the world, including Edinburgh, London, Cardiff, New Delhi, Manila, Hong Kong, Brisbane, Tokyo, Belfast, Dublin, Newcastle, Brussels, Madrid, LA, San Francisco, Miami and Chicago.
Those who can't make it to any of the official events are encouraged to host their own, with the goal of involving as many people as possible in the quest to secure somewhere to live as a basic human right that's respected across the globe.
What are the rules of the Big Sleep Out?
For health and safety reasons, the event is only open to those aged 16 or over. No alcohol is permitted on the site of the Big Sleep Out and there will be no bars either.
Since December is cold in the UK, you're advised to wear warm, waterproof clothing, including a hat and a pair of gloves, and bring a sleeping bag appropriate for the overnight temperatures.
You might also wish to bring a camping mat, but you're not permitted to bring a tent given that the challenge is to sleep outside without any cover.
What facilities will there be at the Sleep Out?
There will be toilets on-site, as well as free hot drinks throughout the event, and a range of food trucks for hot street food.
You'll also find warming stations, medical services in case you're not feeling well, and overnight security.
Where are the UK events taking place?
The Big Sleep Out will take place across the planet on Saturday 7 December.
Doors open at 5.30pm and there will be no further admittance after 8pm.
There are Sleep Outs taking place in the following locations:
Edinburgh - Princes Street Gardens
London - Trafalger SquareNewport, Wales - Rodney Parade
Belfast - Stormont Estate
Cardiff - Cardiff Castle
Brighton - Hove Lagoon
Manchester - Lime Square
What entertainment will there be?
At many of the Sleep Out events there will be a programme of entertainment, with a bedtime story and musicians.
At the London event, Helen Mirren will tell a bedtime story and Travis will perform an acoustic set. Other acts include Tom Walker, Rag 'n' Bone Man, Jake Bugg and Gang of Youths.
Gregor Fisher will tell the bedtime story at the Edinburgh event, and there will be music from Izzi Bizu, Daniel Portman, Angie McMahon, Ensemble and the Salvation Army Choir.
In Belfast, Ragair, Runabay, Vinci and Fallen Lights have been confirmed, while Kenney Jones will perform at the Brighton Sleep Out.
Charlotte Church will take the stage in Cardiff and the bedtime story will come from Ruth Jones. Other acts include Matthew Pritchard, Boy Azooga, Patrick Jones, Kizzy Crawford, Dr Beverly Ballcrusher, The Gentle Good and Shellyann.
How can I get involved?
Whether you want to attend an official event or get set up one of your own, all of the details can be found on the Big Sleep Out website.
Tickets for the UK events cost £15, with 100% of the funds raised going towards registered charities helping homeless and displaced people.
Only participants who have pre-registered may attend with the ticket issued in their name.
Anyone without a ticket who hasn’t registered won't be admitted.