By the close of this century the world may have to feed as many as 2 billion additional people. Most of them will be born in developing countries, especially in marginal lands ill-suited for food production. This article focuses on efforts by the International Agricultural Research Centers to increase food production in the Third World and addresses the social and ecological issues raised by the introduction of high-yielding varieties into fertile Third World lands and describe how varieties are being tailored for introduction into marginal areas.