Prince William is launching a major five-year campaign to end homelessness, which he says should not exist in a "modern and progressive society".
The Prince of Wales's charitable foundation is putting in £3m of start-up funding to help make homelessness "rare, brief and unrepeated".
Six locations across the UK will be used to test ideas to cut homelessness.
"Everyone should have a safe and secure home and be treated with dignity," says Prince William.
This "Homewards" initiative is likely to be one of the defining projects for the Prince of Wales - a commitment which he will be aware comes with the risk of being accused of straying into politics.
Ahead of the launch, Prince William has spoken to Labour leader Sir Keir Starmer, Levelling Up Secretary Michael Gove and the first ministers of Scotland and Wales.
It is a cause that is deeply personal to the prince, which he has linked to the influence of his mother, Princess Diana, who brought him to homelessness charities as a child.
There are more than 300,000 people currently homeless across the UK, which includes those who are stuck in hostels and temporary accommodation, living in cars and sofa-surfing, as well as people who are rough sleeping.
As well as preventing homelessness, there is an aim to change attitudes and show how many people can be affected. Recently the prince opened an affordable housing project for young people with jobs, but who still needed help with accommodation.
Prince William's plan is to bring together local coalitions of housing experts, charities and private industry to develop housing projects and support services, addressing different ways that homelessness occurs, whether in big cities or coastal towns.
He will be holding a two-day whistle-stop tour of the UK revealing the locations for the initiative, which is backed by charities such as Shelter, Centrepoint, Crisis and The Passage.
A media briefing was told that success would be measured in terms of lowering homelessness in those places - and finding approaches that could be replicated elsewhere.
He has also drawn international inspiration from Finland, seen as a model for reducing homelessness to very low levels.
The campaign has published opinion polling from Ipsos of more than 3,000 adults in the UK, which suggests the level of public concern and support for an intervention.
But Prince William will also face challenges about how someone with such wealth and extensive property holdings can make such calls over homelessness.
"The last thing we need is for William to get involved in this issue, a man who has three huge homes and a vast estate gifted to him by the state," says Graham Smith, of the anti-monarchy group, Republic.
He says homelessness is about government policy and investment and will not be "resolved by charity or royal patronage", accusing Prince William of being "hypocritical".
But a Kensington Palace spokesman said it was about the prince using his public platform to make a positive difference.
"This isn't about a PR stunt. This is about trying to change the way that we as a society think about homelessness," said the spokesman.
Matt Downie, chief executive of the charity Crisis, said he had personally spoken to the Prince of Wales about the project and endorsed the authenticity of his commitment.
"People who are experiencing homelessness can smell when someone's not authentic. I certainly can see the difference between people who want to associate for PR purposes in this issue and people who are genuinely driven by righting one of society's wrongs, and I saw that deeply there," said Mr Downie.
Royal author and academic Prof Pauline Maclaran said such an activist approach was likely to go down well with a younger generation, who were more likely to question the value of the monarchy.
But she said it would need the prince to be seen to make a personal contribution. His Royal Foundation is providing £500,000 in seed funding at each of the six regional centres for the project, but so far there has been no confirmation of earlier reports of social housing plans for his Duchy of Cornwall estate.
Historian Sir Anthony Seldon said Prince William's initiative showed how royal interventions could look beyond short-term political cycles at wider issues such as "the mental health and welfare of the population, the physical and built environment, and the economic condition of the people".
But he said it meant the prince was "squarely in the space normally reserved just for elected politicians".
Political parties are already sparring over the response to rising mortgage and rent costs and a lack of affordable housing.
Cllr Darren Rodwell, housing spokesperson for the Local Government Association, said councils feared a "national homelessness crisis" - and there were 1.2 million people on council waiting lists for housing in England.
He said there was a perfect storm of "depleting housing stock and an unaffordable and overly-competitive private rented market" and renters facing eviction - and he called for councils to be able to build 100,000 new social rent homes each year.
But Prince William said he was confident about the ambition to fundamentally reduce homelessness.
"I want to make this a reality and, over the next five years, give people across the UK hope that homelessness can be prevented when we collaborate," he said.
A spokeswoman for the Department for Levelling Up, Housing and Communities welcomed the prince's initiative.
"We are giving councils £2bn over three years, to help them tackle homelessness and rough sleeping, targeted to areas where it is needed most," she said.