World population, currently approaching 7.5 billion, will probably exceed 11 billion by the end of the century, almost double what it was at turn of the present century. The growth is uneven, and the result is a redistribution of the world's population: at the end of this century Europe will have essentially no more people than it had fifty years ago, whereas Africa's population will have multiplied 20-fold, and will have gone up from under 10% to over 30% of the world's population. Thus, not only is population growing but it is currently growing in those regions of the world that have the least resources at their disposal, and the result is liable to be a dramatic rise in world inequality; increased conflict over access to resources; and increased migratory pressure from the poor to the richer regions of the world. In this introductory chapter, we discuss the history and sources of growth in world population over the past two centuries (in particular mortality and fertility) and its eventual stabilisation. We consider some of the major links between population and social dynamics in the light of two basic approaches to world population growth: The Malthusian approach, which views growth as a catastrophe, and the Marxian approach, which sees both population growth and its outcomes as contingent on social conditions and responses. We focus on the mutual relationship between population and societal change at all levels, the micro-, the meso-and the macro-levels, a relationship that is also reflected in the papers in this collection. However, there is also agency in population growth and the introduction concludes with a consideration of the options which humanity faces given the anticipated growth of world population and its redistribution.