Normally, you are required to present a passport from your country of citizenship or your refugee travel document to travel to a foreign country. Additionally, the foreign country may have additional entry/exit requirements (such as a visa).
At a port of entry, an Officer will review your green card and any other identity documents you present, such as a passport, foreign national I.D. card or US Driver’s License, and make a decision if you can enter the United States.
As a green card holder, you are free to travel outside the US, and traveling outside the US temporary or briefly usually does not affect the permanent resident status. If you did not intend to make the US your permanent home, you will be found to have abandoned your permanent resident status. It is whether you have been absent from the United States for more than a year.
While traveling outside the US for a brief trip generally are not problematic, the immigration officer may consider criteria such as whether your intention was to visit abroad only temporarily, whether you maintained US family and community ties, maintained US employment, filed US income taxes as a resident, or otherwise established your intention to return to the US as your permanent home. Other factors include whether you maintained a US mailing address, kept US bank accounts and a valid US driver’s license, own property or run a business in the US, or have any other evidence that justifies the temporary nature of your absence.
If you plan on being absent from the US for longer than a year, it is advisable to first apply for a reentry permit by filing Form I-131. Getting a reentry permit prior to leaving the US allows a permanent or conditional permanent resident to apply for admission into the US during the permit’s validity without having to get a returning resident visa from a US Embassy or Consulate abroad. However, it does not guarantee entry into the US upon your return as you must first be determined to be admissible. But it will certainly be of help in establishing your intention to permanently reside in the US.
If you remain outside of the US for more than two years, any reentry permit granted before your departure from the US will have expired. Under such circumstance, it is advisable to apply for a returning resident visa (SB-1) at the nearest US Embassy or Consulate. An SB-1 applicant has to establish eligibility for an immigrant visa and will need to take a medical exam. If you are the spouse or child of either a member of the US Armed Forces or civilian employee of the U.S. Government stationed abroad on official orders, there is an exception to this process.
Additionally, absence from the US for periods of six months or more may disrupt the continuous residency essential for naturalization purposes. If your absence is one year or longer and you want to preserve your continuous residency in the US for the sake of naturalization, you can file an Application to Preserve Residence for Naturalization Purposes (Form N-470).