After the marriage petition is filed, the USCIS will issue a receipt notice. At the interview, the USCIS officer will question you and your foreign spouse in detail with respect to the specifics of your marriage in order to determine its legitimacy. Further, you and your foreign spouse will be required to provide documentation demonstrating the legitimacy of your marriage. Once the USCIS officer determines that you are lawfully married, s/he will approve the marriage petition. Then the USCIS officer will decide the application for permanent residence. Currently, the permanent residence interview is scheduled (on average) within 4 months of filing.