For most lawful permanent residents (LPRs) it is required that they maintin their primary place of residence within the United States.  If an LPR takes long trips abroad, or spends more time abroad than in the US, the Department of Homeland Security (DHS) may determine that the LPR has abandoned their permanent resident status.  This results in the loss of one’s greencard.  DHS takes many factors into account when making this determination.  Generally it is avised that LPRs do not take trips abroad of 6 months or more in duration.  In emergency circumstances where return before 6 months is not possible, an LPR should take care to acquire documents proving those circumstances.  Having employment abroad, unless it is for certain US government agencies or part of US millitary service, can contribute to a finding of abandonment.