Sorry for yet another dumb-*** question. But what is API? I haven't been on a plane since the end of 2006, and didn't use any kind of online check in then, and it's obviously got more complicated than I thought. I understand what ESTA is, and have no worries about that, it's basically your green waiver form but online. (Although at the moment you still do both). I have seen people on here talking about "doing their API" and I think I saw something listed as API on my Virgin Atlantic booking page... but can someone help me with an idiots guide as to what it is? Many thanks!!