Naturalization is the process by which lawful permanent residents become U.S. citizens. Requirements include being at least 18 years old, having continuous residence for five years (three years if married to a U.S. citizen), demonstrating good moral character, passing English and civics tests, and taking an oath of allegiance. Naturalized citizens enjoy full rights including voting, holding public office, and obtaining a U.S. passport. The process typically takes 6-12 months.