I need help, I'm trying to help out a friend from South Korea. He wants to visit the US and has a Korean passport. But I'm not sure if he needs to get a visa before purchasing a plane ticket or if its even required? He is coming here for about 4 weeks to visit. If he does require a visa, what is the process of acquiring one. Does he get it done when he lands in the US or is this supposed to be done way in advanced before he purchases a plane ticket? I've tried looking online and there are some people that say a visa isn't required and some say that it is. Any help is appreciated. Thank you!