When an immigrant comes to the United States on a K-1 visa and marries a U.S. citizen or permanent resident, the immigrant receives a conditional green card. (The K-1 immigrant's children that come to the U.S. with a K-2 visa may also receive a conditional green card after the marriage.) A conditional green card expires after two years.
The conditional green card is like a probation period for two years during which the couple builds a record of their married relationship together. At the end of that period the couple files Form I-751, Petition to Remove Conditions on Residence, in addition to evidence of their good faith marriage.
The conditional two-year period is in place to help prevent marriage fraud. Therefore, couples should take the filing process very seriously as it is more than just filing a form. The couple must Prove a Good Faith Marriage.
Upon approval of the I-751 petition, the permanent resident (along with any children that filed on the same petition) will become lawful permanent residents with 10-year green cards.