Father Ratzinger's work is intended to establish the general guidelines for a discussion of the meaning of the term ""Christian brotherhood."" The book is divided into two parts: an historical analysis, which discusses the genesis of the concept of brotherhood in Hellenistic philosophy and in the Old Testament and traces its development in the primitive Church; and a synthesis, presenting the concept of specifically Christian brotherhood which has as its basis a community of faith. It is not possible, obviously, to overestimate the importance for the ecumenical movement of a mature and realistic approach to the meaning and implications of Christian brotherhood, and this small book meets that need admirably. It is not intended to be a definitive treatment of the subject so much, as the author says, as ""an invitation to discussion."" On that basis, The Open Circle is recommended unreservedly as a concise and highly readable introduction to a concept of tremendous significance for the future.