Im flying from London to Buenos Aires via Washington, do I need a Transit Visa?
GOPBI has given you the right answer; let me just add: you don’t need to fill the flight details or address columns, those are not mandatory. You may enter in the address column “in transit to Argentina”. https://help.cbp.gov/cgi-bin/customs.cfg… .. https://esta.cbp.dhs.gov/esta/WebHelp/ES… .. And use the official link GOPBI has provided; some fraudulent agencies want to make money by just providing links to the U.S government site and they are asking for a fee of up to £30 for doing so.