Through a 'jus sanguinis' policy, one is conferred citizenship based on ancestry or ethnicity, and is more related to the concept that is common in Europe. Children whose parent(s) are US citizens can claim citizenship through their status as citizens. The process is a bit complicated and long winded and also depends on the laws at the time the child was born. However, any one born in the United States automatically becomes a US citizen.

Filing Form N 600, Application for Certificate of Citizenship:

It is important to remember that if you were born in the US, you can just apply for a US passport to have as a proof of your US citizenship status. Should you need to document your status based on citizen parentage, you may file Form N 600, Application for Certificate of Citizenship with the USCIS. The road to travel is a bit rocky as it generally requires a combination of at least one parent being a U.S. citizen when you were born and having lived in the U.S. or its possessions for a period of time.

As mentioned earlier, you can become a U.S. citizen through your parents' status once certain conditions are satisfied. To qualify, you have to be below the age of 18 and at least one of your parents have to be a U.S. citizen, either by birth or through naturalization. You should reside in the US in the legal and physical custody of your U.S. citizen parent subject to lawful admission for permanent residence.

But qualifying as a "child" has its own norms. To qualify as a "child"to get a certificate of citizenship through your parents' status, you should NOT be married. Also, if you were born out of wedlock, you should have been "legitimated" while you were below 16 years old and while you were in the legal custody of your legitimating parent. Not a hard rule this, but a stepchild who was not adopted will not be eligible or qualify as a "child" under this category. If you are affirmative to the above mentioned statements or meet these requirements before turning 18, you automatically obtain US citizenship without even having to file an application. But remember, you will have to file Form N 600, Application for Certificate of Citizenship with the USCIS,

The Child Citizenship Act does not grant or allow citizenship for individuals who were age 18 or older on February 27, 2001. One who was over the age of 18 as on February 27, 2001, may have qualified to apply for a certificate under the earlier law in effect before the CCA was enacted.

So this brings us to the next question. What difference it would make if you lived outside the United States? The laws mentions that biological or adopted children who regularly reside abroad may qualify for naturalization. But you have to cater to the eligibility requirements to get a citizenship certificate. At least one of your parents should be a U.S. citizen or, if deceased, your parent was a U.S. citizen at the time of hes/her death.

Adding further, your US citizen parent should have been physically present in the US or its outlying possessions for at least five years, out of which two were after you reaching the age of 14. Not to forget that you have to be under 18 years of age. Additionally, you should be residing abroad in the legal and in the physical custody of the U.S. citizen parent. Lastly, you are temporarily present in the US after having entered lawfully and are maintaining lawful status here.