In forty years the world's population has doubled, and experts predict it will nearly double again (to ten thousand million) in. the next fifty. Meeting the needs of so many people will require a five to tenfold increase in economic activity, and doubts are growing that the earth can sustain this. On the basis of the author's informed and lucid survey of the various "perils" of the population question it is not surprising that churches, like the human family as a whole, are deeply divided over what to do about it. After an overview of responses already being made by churches and the ecumenical family, he proposes some theological resources and ethical guidelines for shaping a Christian approach to a critical and difficult contemporary issue.