I'm a U.S. citizen and resident. I'm going to be attending a conference in Spain in September. I started to fill out the registration form, and one of the questions is, "Do you require a visa letter?"
How do I know if I require a visa letter? The conference is work-related, but hosted by a non-Spanish company, and I won't be making any money off the trip.
ETA: if it makes a difference, I'll only be there for a week.