For millions of lawful permanent residents in the United States, holding a green card is often the first step toward full citizenship. The final stage of the journey is naturalization, a process overseen by U.S. Citizenship and Immigration Services ( USCIS ) that includes eligibility checks, background screening, interviews and testing. Most green-card holders must wait five years before applying for citizenship. Those married to U.S. citizens may qualify after three years, provided they have