This study offers a fresh reappraisal of the philosopher, political thinker, and historian of ideas Sir Isaiah Berlin (1909-1997) from childhood to the height of his intellectual career. It provides the first historically contextualized study of Berlin's formative years and identifies different stages in his intellectual development, allowing a reappraisal of his theory of liberalism. Applying a 'double perspective' that examines Berlin both as an East European Jewish émigré as well as a British Liberal intellectual, author Arie Dubnov stresses the very ambivalent relation between Berlin's liberal philosophy and his pro-Zionist sentiments.