In Denmark you can have an unlimited number of first names, but you must have one, an unlimited number of middle names and exactly one surname. How you refer to someone is, I'd say, up to the person being referred to. Michael M?rk?v isn't being referred to by his surname, but by his first and middle name. (Probably) no one would know who you referred to if you called him Michael Christensen. The same way Michael Valgren is referred to without his surname. On the other hand someone like Chris Anker S?rensen is being referred to by all of his first name, middle name and surname (I think Anker is a middle name to him, but it can be his second first name as well, or, for another person, a surname. That's right you could be named Anker Anker, I don't know if you could be named Anker Anker Anker as well, but I don't think so.).