More than 1.1 billion people worldwide officially don't exist, going about their daily lives without proof of identity.
The issue leaves a significant fraction of the global population deprived of health and education services, particularly in geographical areas whose residents face poverty, discrimination, epidemics or armed conflicts.
Among these "invisible people," many of whom live in Africa and Asia, more than one third are children whose births have not been registered, the World Bank's "Identification for Development" (ID4D) program recently warned.
Vyjayanti Desai, who manages the ID4D program, said the issue arises from a number of factors, but cited the distance between people and government services in developing areas, where it may take hours to reach administrative service, as major.
Many families are also simply not informed about the importance of birth registration, and the consequences of non-registration, which can include the denial of basic rights and benefits, or an increased likelihood of marrying or entering into the labor force underage.
And even if parents are aware of the need to declare a birth, costs can be crippling, said Anne-Sophie Lois, representative at the United Nations in Geneva and director of the children's aid organization Plan International.
Political climate also discourages many families from allowing themselves to be officially identified, if the government preferences one ethnic group or nationality.
Beyond being barred from attending school, these children can fall prey to violence ranging from forced labor for boys to early marriage for girls, denounced by UNICEF in a 2013 report.
"The legal invisibility of unregistered children makes it more likely that their disappearance and exploitation will go unnoticed by authorities," Lois said.
To combat this immense problem, organizations are patiently working on the ground to identify these "invisible" people.
Digital technologies have provided a tremendous boost, Lois said, as a way to "increase registration, provide legal documentation of vital events and produce statistics that are complete and accurate."
The World Bank recognizes, however, that centralized identification systems could expose vulnerable groups to risks linked to misuse of their personal data.
"We are very cautious," Desai of ID4D emphasized. "To have a legal framework in place that protects privacy and personal data is key."