This book is a study of the category of definiteness in the light of research on mental spaces and frames. The author formulates a set of eight uniform rules for the use of the definite, indefinite, and zero articles in English and German. "The Concept of Definiteness" presents an algorithm for nominal reference resolution that uses the definiteness value of each noun phrase to guide the search for its referent. The book discusses the results of the application of an automated system based on the proposed algorithm to texts in modern English. It also demonstrates applicability of the selected approach to text fragments representing all major historical variants of the German language.