We are used to calling most developing countries overpopulated and consi dering some industrialized countries (like West Germany) "threatened by underpopulation". Analogous population policies with different objecti ves are discussed. However, none of the measures suggested can be justi fied or evaluated without an implicit concept of optimum population, a notion which has attracted attention ever since economics was made a science. The relevance of the subject and the recent rise in interest b ...