  First: When you travel under the VWP for business or tourist purposes and you do not have a visitor visa, you are required to apply for an ESTA. Second: You must also apply for an ESTA if you do not have a visitor visa but you have another type such as an F0 student visa and you are travelling under the VWP for short-term business or tourism. Finally: You will not need to apply for a Travel Authorization (ESTA) when travelling on short-term business or tourism under the VWP and you already have a visitor visa (B0/B0).  First: When you travel under the VWP for business or tourist purposes and you do not have a visitor visa, you are required to apply for an ESTA.  Second: You must also apply for an ESTA if you do not have a visitor visa but you have another type such as an F0 student visa and you are travelling under the VWP for short-term business or tourism.  Finally: You will not need to apply for a Travel Authorization (ESTA) when travelling on short-term business or tourism under the VWP and you already have a visitor visa (B0/B0).  