Born abroad? You might not be welcomed aboard. To gain U.S. citizenship, applicants might need more than an American parent. This explainer walks you through the laws that surround this week’s show, Left by the Ship (airing May 24 on Independent Lenscheck local listings).

If you know anyone who’s applied for U.S. citizenship, you’ve heard it’s a byzantine process. For Amerasians, born in Asia to a U.S. military father and an Asian mother, it’s even more Kafkaesque. This week’s show, Left by the Ship (airing May 31 on Independent Lens), features Amerasians who were left behind by their U.S. servicemen fathers in the Philippines and excluded from the 1982 Amerasian Homecoming Act. Unlike the Amerasians born in Vietnam, Korea, Thailand, Laos, or Kampuchea, half-Filipino and half-Japanese children must be claimed by their American parent to get U.S. citizenship. Congress supposedly chose those countries because of their relative poverty, and many writers have expressed outrage that the Philippines was left off the list.

So how do Amerasians — including those born in born in Vietnam, Korea, Thailand, Laos, and Kampuchea — qualify for citizenship under the 1982 Amerasian Homecoming Act? They need to look the part. The law states that a naturalization director determines “whether there is reason to believe the beneficiary was fathered by a United States citizen.” That means a judge can decide if they are mixed race by appearance alone. As you can imagine, this leads to contentious cases, such as that of Nguyen Thanh Hien covered in Time magazine. Despite his thick facial stubble that earned him torment in Vietnam, a judge ruled that Hien was not mixed race.

What about everyone else born abroad to one American parent? If the parents are married, the rules are straightforward: the U.S. citizen parent must have lived in the states for any amount of time. If the child is born out of wedlock, the requirements get trickier, and they’re more stringent for an American father than mother. The father and child must prove a blood relation (i.e. a blood test), the father must have lived in the U.S. five years (two of those after he was 14), and he must agree to support the child until the age of 18. Phew! If the mother is the U.S. citizen, she only has to have lived in the U.S. for one year.