Even without the ban in place, US-funded programs don't perform abortions - that's already ruled out - but they can give provide information. Now with the ban, if they really want to do that, no matter who pays for it, the US government will cut them off.
The policy also prohibits taxpayer funding for groups that lobby to legalise abortion or promote it as a family planning method.
While the ban is a blow to reproductive rights - it's a policy that's been seen before - the setting in which the new President chose to stage its reinstatement has abortion activists outraged.
With his Vice President and staff looking on, the President sealed the deal on the "global gag rule" - there didn't appear to be any women alongside the president when he did so.
The policy has been instituted by Republican administrations and rescinded by Democratic ones since 1984.
Most recently, former President Barack Obama ended the ban in 2009, and Trump of course made it a priority to move against it.
The World Health Organisation estimates 21.6 million women a year have unsafe abortions in developing countries, accounting for 13 per cent of all maternal deaths.