The laws of most countries permit individuals who meet eligibility requirements to apply for citizenship by naturalization. You may become eligible to apply for citizenship by naturalization due to your ancestry, your marriage, your ethnic background or religion, or legal residence in the country for a period of years. The period of legal residence required before you can apply for naturalization varies widely from country to country, ranging from a low of two years in Australia to a high of at least twelve years in Switzerland. The period is three years in Canada and New Zealand; and five years in Ireland, the U.K. and the U.S.. In some cases, the period can be shortened if your spouse is already a citizen.
Every country has the right to determine who are its citizens. Typically, most people acquire at least one citizenship at birth. In many countries, a baby automatically becomes a citizen of the country at birth if he is born in that country regardless of the status of his parents. A child born in the U.S., for example, is a U.S. citizen even if both of his parents are illegal immigrants. The only U.S.-born children who are not U.S. citizens are those born of a parent who is serving as an ambassador or diplomatic representative of a foreign country in the U.S..
The U.S. also generally gives citizenship at birth to a child born abroad if one or both of his parents are U.S. citizens when he is born. At least one of his parents must have resided in the U.S. sometime before the child was born. If only one of the child’s parents is a U.S. citizen and the child is born abroad, the child becomes a U.S. citizen if the citizen parent was ever physically present in the U.S. for at least five years, at least two of which were after the citizen parent was 14 years old.
In some European countries, including Germany, for example, a child obtains citizenship only if at least one of his parents is a citizen when he is born. His place of birth is immaterial. Hundreds of thousands of German-born children of Turkish parents have until very recently never been able to acquire German citizenship even after living in Germany their entire lives. Under a recent change in German law, some of these children will now be given a one-time opportunity to elect German citizenship after they become of age. Those who so elect will lose their Turkish citizenship since Germany does not permit dual citizenship.
You get your first citizenship automatically at birth from one or both of your parents or because you were born in that country. You do not choose your first citizenship any more than you choose your religion. You have it whether you like it or not unless and until you renounce it or otherwise lose it.