The world must do more to confront the largely unstudied and neglected phenomenon of people-trafficking, the United Nations has said in a report.
So little is known about the problem, says the report, that no estimate can be given of the number affected.
The report also points to a more basic problem: the lack of a common understanding of what human trafficking is, and whom it affects.
But it is "a crime that shames us all", said the UN's Antonio Maria Costa.
In the report - "Global Report on Trafficking in Persons", released by the UN Office on Drugs and Crime (UNODC) - the UN paints a picture of a shadowy form of human slavery little understood by governments, and only rarely adequately tackled.
The report points out that the most commonly used term for the problem - "people-trafficking" - itself emphasises the transaction aspects of the crime, rather than the day-to-day experience of modern enslavement.
And it suggests the trafficking phenomenon is little understood in all its forms from child soldiering to sweatshop labour, domestic servitude, and even entire villages in bondage.