First published in 1998. In this book the author presents the view that although many linguists have been interested in specific indefinites, their theories are not quite satisfactory in that they have only tried to explore some aspects of specific indefinites. This paper assumes a standard notion of specificity, i.e., the notion of someone having-in-mind an individual or a relation. Under this assumption, there is an attempt to review previous studies on specific indefinites, and propose a new theory of specificity which I believe can capture all aspects which the previous studies have explored. This leads us to a new information theory which is partially representational and partially denotational., and which is useful for dealing with conversational aspects, like the distinction between the speaker and the audience.