While the ecumenical movement is still an object of fear for a considerable number of Christians it has become a scandal and a stumbling block for many others. The former see it as a threat to their religious identities, the latter as an obstacle to their missionary zeal. This book envisages both the fearful and the disillusioned and attempts an analysis which should enable the movement to know itself better and to renew itself more effectively and thus to again the universal confidence and support which it deserves and needs. Theology of Ecumenism is the result of reflection on the operations and processes involved in the ecumenist's work of promoting Christian unity. As such it is a pioneering piece of work and might have been subtitled an essay in methodology'. Its theology of Christian cooperation as the achievement, however partial, of the end-unity in mission-land its critical remarks on the nature of 'ecumenical theology' are of particular significance.