By Alex Kirby
BBC News Online environment correspondent
The number of people living out their days in the squalor of a slum is almost one billion, the United Nations says - one-sixth of the world's population.
The 1990s saw a rapid rise in slum dwellings, report says
Without radical changes, it believes, that number could double in 30 years.
By 2050, the UN says, there may be 3.5 billion slumdwellers, out of a total urban population of about six billion.
The head of its human settlements programme says the persistence of slums should shame the entire world.
The programme, UN-Habitat, has compiled what it says is the most comprehensive report ever on slums, based on studies of 37 cities across the globe.
The report, The Challenge Of Slums: Global Report On Human Settlements 2003, is published on 6 October, World Habitat Day.
In 2001, it says, 924 million people, 31.6% of the world's urban population, lived in slums, most of them in developing countries.
The report says the number of slumdwellers almost certainly increased substantially during the 1990s. But it says national approaches have generally moved away from "negative policies such as forced eviction, benign neglect and involuntary resettlement".
Instead, it says, the emphasis is increasingly on self-help, upgrading existing slums rather than resettling their inhabitants, nurturing the abilities of the people who live in them, and respecting their rights.
The report treads some familiar ground in its prescriptions for change. Policies, it says, "should more vigorously address the issue of the livelihoods of slumdwellers and urban poverty in general".
They should be as inclusive and accountable as possible, and should involve slumdwellers themselves in identifying their problems and implementing the solutions.
The report stresses the importance of providing security of tenure (though not necessarily outright ownership) to persuade people to invest in their communities.
The executive director of UN-Habitat is Dr Anna Tibaijuka. She told BBC News Online: "On policy, our first solution is to reiterate the need for political will.
ESTIMATED SLUM POPULATIONS
Sub-Saharan Africa 71.9%
"We should all be ashamed to have these unplanned neighbourhoods in our cities.
"One of the UN's millennium development goals committed world leaders to achieving 'significant improvement in the lives of at least 100 m slum dwellers by the year 2020'.
"Once we accept the principle that underlies that goal, I'm convinced we shall achieve it.
"And we have to recognise that the poor are an asset, hardworking and decent people. But with policies that discourage them, how do we expect them to improve their lot?"
The report expresses concern about globalisation, saying current evidence suggests in its present form it "has not always worked in favour of the urban poor".
EFFORTS TO BEAT POVERTY
Read the key points and see graphs from the UN's Human Development Report 2003
Dr Tibaijuka told BBC News Online: "Globalisation is a work in progress, and it needs to be regulated. We have to try to maximise its benefits - it would be naive to say there's nothing we can do to control its downside."
Speaking at the report's London launch, Professor Patrick Wakely of University College London said: "I was in a slum recently in Surabaya, in Indonesia.
"Someone pointed out the shoes I was wearing had probably been made in that slum itself. Globalisation can offer opportunities that weren't available in the past."