The travel validity period of a green card is one year – this means that both legal permanent residents and conditional residents (hereafter “residents”) can be outside of the United States for up to one year without having to file any additional paperwork to get back in. The issue arises when a resident will be out of the country for longer than one year. In this circumstance, the resident faces a risk of denial of admission back into the U.S. on the grounds of having abandoned his or her permanent resident status.
A reentry permit, which is generally valid for two years from the date of issue, is obtained by filing form I-131 from within the United States. Although the USCIS is willing to ship the reentry permit to a U.S. embassy or consulate abroad, the application for the reentry permit must begin when the resident is inside the U.S. While departure from the U.S. before a decision is made will not affect the application, be certain to take care of biometrics collection before departure to avoid possible denial.
Another important consideration when travelling outside of the U.S. as a permanent resident is continuity of residence for the purpose of naturalization. Typically, an absence of more than 1 year from the U.S. will break the continuity of residency required for naturalization, and the reentry permit will do nothing to change that. If you must leave the country for longer for certain employment arrangements and do not want to restart the residency timer for naturalization, you must file an Application to Preserve Residence for Naturalization Purposes (Form N-470).