The subject of this book is the Hittite prohibitive expression, natta Ura - 'not allowed', 'not correct'. This expression, studied here in a full contextual and semantic approach, prohibits over twenty different social behaviours. It touches upon matters of sexual conduct, religious observances, political injunctions and ethics. The study questions how the authoritative and punitive institutions in the land of Hatti utilized this expression in order to define and articulate various prohibitions and what role did these prohibitions play in the legal and moral systems of the Hittites. The aim is to describe what the Hittites thought of as forbidden or taboo and by so to achieve for the modern scholar a sharper image of some of the distinctive traits of Hittite society. The study is intended primarily for Hittitologists and Assyriologists but it will appeal to other audiences such as biblical and classical scholars, and to those interested in the social history of ancient societies.