This book was first published in 1935 under the title of The Catholic Eastern Churches. It has now been stringently revised and, so far as difficult times allow, brought up to date, and is republished with its fellow on the Dissident or Separated Eastern Churches. The two books are intended as a modest and elementary contribution for English-speaking people to the wider spreading of knowledge about the Christian East; familiarity with whose history, religious life, and present state was so often urged on Catholics (and by implication another Christians) of the West by the late Pope Pius XI.