The ICAO standard says a passport must have a field labelled "sex" containing F, M or X; in this context, X means "unknown" or "unspecified". About a dozen coun

The ICAO standard says a passport must have a field labelled "sex" containing F, M or X; in this context, X means "unknown" or "unspecified". About a dozen countries will issue passports with an X in the "sex" field, but I'm not sure which of them, if any, will do it for anyone who asks for it, which seems to be what's proposed for the US. The really radical thing to do would be to only issue passports with an X in the "sex" field. That way non-binary people wouldn't be treated any differently.