<P><EM>On Heidegger''s Being and Time</EM> is an outstanding exploration of Heidegger''s most important work by two major philosophers. Simon Critchley argues that we must see <EM>Being and Time</EM> as a radicalization of Husserl''s phenomenology, particularly his theories of intentionality, categorial intuition, and the phenomenological concept of the a priori. This leads to a reappraisal and defense of Heidegger''s conception of phenomenology. </P><P>In contrast, Reiner Sch¿rmann urges us to read Heidegger ''backward'', arguing that his later work is the key to unravelling <EM>Being and Time</EM>. Through a close reading of <EM>Being and Time</EM> Sch¿rmann demonstrates that this work is ultimately aporetic because the notion of Being elaborated in his later work is already at play within it. This is the first time that Sch¿rmann''s renowned lectures on Heidegger have been published.</P><P>The book concludes with Critchley''s reinterpretation of the importance of authenticity in <EM