A green card is the term for a Permanent Resident Card granted to a foreigner by the U.S. Citizenship and Immigration Services. The card gives the holder the right to live and work in the United States permanently without restriction. With this card and your foreign passport, you are allowed to travel outside the U.S. and return with no additional paperwork.
According to the U.S. Embassy of Mexico, all legal residents of the United States, regardless of their nationality, can travel to Mexico if they are in possession of a green card (now they are pink.) One does not need to go through the process of applying to Mexico City for an entry permit nor do they need to have their passport stamped. A tourist card can be issued on board an aircraft or the port of entry to be able to travel to Mexico as tourists, in transit or for short business trips. You must carry a valid passport and your U.S. Permanent Resident Card (green or pink card) issued by the United States government at all times.
For safety purposes be sure to register at the U.S. Embassy or the nearest U.S.Consulate through the State Department’s travel registration website, in order to obtain updated information on local travel and security. If you are without the Internet, register directly with the nearest U.S. embassy or consulate. Registration allows the State Department to assist or contact a U.S. citizen in case of an emergency.
Also, be sure to research and purchase travel insurance. There is travel medical/evacuation coverage and even travel insurance packages that cover trip cancellations, medical emergencies and medical evacuations. The cost of travel insurance is minimal compared to the medical cost in an emergency situation. Mexico can be a dangerous place in certain regions, be sure to plan for every circumstance and stay safe.
Upon your return from Mexico, you cannot be denied entry. With your valid foreign passport and your U.S. Permanent Resident Card (green or pink card), you have the full right to return to U.S. soil. Be prepared to answer some simple questions and be fingerprinted. If you do not have your passport or green card when trying to reenter the United States, you will be held until the situation can be worked out with the proper embassy authorities, which could take a very long time. For a quick and safe return, be sure not to misplace your passport or U.S. Permanent Resident Card (green or pink card) during your stay in Mexico, keep it with you at all times.