US green card holders are permanent residents of the US and may live and work in the US permanently. They may also travel freely outside of the US. However, if you are a green card holder and want to pursue US citizenship, you are required to maintain a long-term residence in the US without interruptions. If you need to leave the US for work and want to maintain your status so that it does not affect your path to citizenship, you may file N-470 (Application to Preserve Residence for Naturalization Purposes) to ensure that your absence will not harm your chances for citizenship. You must file this form before you leave the US.