There are two ways  to obtain citizenship. 

1. Naturalization is the process by which U.S. citizenship is granted to a lawful permanent resident  after meeting the requirements established by Congress in the Immigration and Nationality Act (INA):

• Be at least 18 years of age old;
• Show that you are a lawfully admitted permanent resident of the United States;
• Have resided in the United States as a lawful permanent resident for at least five years;
• Have been physically present in the United States for at least 30 months;
• Be a person of good moral character;
• Be able to speak, read, write and understand the English language;
• Have and understanding of the fundamentals of the history, and of the principles and form of government, of the United States;
• Demonstrate attachment to the principles of the Constitution and be well-disposed to the good order and happiness of the United States; and,
• Be willing and able to take the Oath of Allegiance.

2. Acquisition  of citizenship is obtained through U.S. citizenship parents either at birth or after birth, but before the age of 18.