A child born to one or both US citizen parents abroad is NOT automatically a US citizen. The child has automatic acceptance as a natural born citizen if, and only if, registered with the nearest US consulate. There is a form to be filed for registration of the birth. Submit that form and the child is automatically approved as a US citizen by birth.Fail to submit that form and the child isnu2019t a US citizen. Having at least one US citizen as a parent is a huge advantage if the child applies later in life, but after the deadline for the form has past itu2019s no longer automatic.Most US citizens register their foreign born children, but not all do so.As to citizenship in the other country, the rules of that other country apply. Not all countries give automatic citizenship by birth in their territory. I donu2019t even think most countries have that rule. Also if one or both parents have citizenship in the country, most countries allow a child to be registered at birth as a citizen.This leaves the possibility that neither parent is a citizen of the country the child is born in. Fail to file that form at the US consulate and itu2019s possible for that child to be a person with no country.Dual citizenship rules vary by country to country as well. US rules about dual citizenship are not well enforced so even if it breaks the US rules people can end up dual citizenship. US rules generally allow dual citizenship by birth, with certain events triggering a need to chose. Again, those rules arenu2019t well enforced.