This book revisits the theory of social systems as a defence against anxiety first set out by Elliott Jaques and Isabel Menzies Lyth in papers which they published in 1955 and 1960, and which have been influential points of reference ever since. Menzies Lyth's study of the nursing system of a general hospital, with its roots in both psychoanalysis and socio-technical systems thinking, has remained one of the most convincing demonstrations of the influence of unconscious anxieties on social behaviour, and of their effects in inducing dysfunctional defensive systems in organisations. The theory of 'social defences against anxiety' remains one of the most significant contributions of the 'Tavistock school' to the study of human relations. Contributors explore this theory as a generative paradigm, capable both of theoretical extension and of empirical application to different institutional settings. They review changes which have taken place in the theoretical and social context since these ideas were first advanced, and assess what conceptual revisions these developments require.