New paperback edition. The work of Wilfred Bion, by its very nature being a major step forward in the psychoanalytical model making of the mental apparatus, will undoubtably require many years for its full assimilation into the thought and practice of workers in the field. To assist this process of assimilation two types of exposition are required: to help students read Bion's work in a comprehending way; and to show the way to the clinical application of this revolutionary modification of the working mosel of the mind.