Oct 30, 2014 living
One can work as a postdoc in US with two types of visa: J-1 and H-1B. No matter which type, she is required to apply for a Social Security Number, or SSN in short, ten days after her entering US. SSN is used for the US government to record her salary payment for tax purpose. It is also needed for many other services, optionally or mandated, such as driving test, enrollment of health benefits, etc. One can find a nearby agency on http://www.ssa.gov/ssnumber/ to apply for it. The ten-day period is needed for her entrying information being updated in the government’s system.