"Even in such open-minded cities, undead must often submit to a process of authorization in order to have unrestricted legal access to the metropolis. An undead with recognized feeding requirements (notably vampires, but also other undead) must obtain an authorization for a given length of time (which varies by locale or even precinct, but usually must be renewed at least once a year). This authorization requires the undead to show, in detail, how it will meet its feeding needs for the given period in a way that does not involve harm to other citizens, visitors to the locale, or citizens of other locations that could find fault with the city’s harboring the undead in question. Most such plans revolve around the purchase of livestock from which the undead obtains sustenance."
— Dungeons & Dragons, "Libris Mortis: The Book of Undead, Chapter 1 All About Undead"