If the mother is an American, it's not complicated. There are other cases, but the "both parents are American citizens" case is pretty straightforward.

Those requirements boil down to this:

- One parent must be a citizen.

- That parent needs some connection to the US, measured by how much time they've spent living there.

- If the citizen parent is male, he must prove that the child is related to him.

- If the citizen parent is male, he must swear a binding legal oath to financially support the child.

The rest resolves these questions:

- How much residential connection to the US must citizen parents have, based on the couple's total Americanness? (more Americanness, less time)

- Can we just assume that married men are the fathers of their wives' children? (yes)

- What counts as being "in America"? (government service abroad counts)