The global population has increased by two billion over the last 25 years, surpassing the 7 billion mark in late 2011. It is likely to increase by at least another two billion by 2050. Beyond the sheer numbers, the world is faced with unprecedented diversity in demographic situations across countries and regions, as well as within countries. Such diversity is mostly found in evolving demographic structures and the changing proportions of youth and elderly groups, and in different rates of fertility, morbidity and mortality, population growth, urbanization, and internal and international migration. More people leads to high demand for environmental products and social services. This unit deals with population dynamics, linkages between population development and environment and policy issues in population, resource management and economic development.