Sub-Saharan Africa as a geographical term refers to the area of the continent of Africa that lies south of the Sahara. A political definition of Sub-Saharan Africa, instead, covers all African countries which are fully or partially located south of the Sahara (excluding Sudan). It contrasts with North Africa, which is considered a part of the Arab world.

The Sahel is the transitional zone between the Sahara and the tropical savanna (the Sudan region) and forest-savanna mosaic to the south. Somalia, Djibouti, Comoros and Mauritania are geographically part of Sub-Saharan Africa, but also part of the Arab world.

Since probably the 5.9 kiloyear event, the Saharan and Sub-Saharan regions of Africa have been separated by the extremely harsh climate of the sparsely populated Sahara, forming an effective barrier interrupted by only the Nile River in Sudan, though the Nile was blocked by the river's cataracts. The Sahara Pump Theory explains how flora and fauna (including Homo sapiens) left Africa to penetrate the Middle East and beyond to Europe and Asia. African pluvial periods are associated with a "wet Sahara" phase during which larger lakes and more rivers exist.

Paul Collier, CBE is a Professor of Economics, Director for the Centre for the Study of African Economies at The University of Oxford and Fellow of St Antony's College. From 1998 – 2003 he was the director of the Development Research Group of the World Bank.

Collier is a specialist in the political, economic and developmental predicaments of poor countries. He was brought up in Sheffield where he attended King Edward VII School. He holds a Distinction Award from Oxford University, and in 1988 he was awarded the Edgar Graham Book Prize for the co-written Labour and poverty in rural Tanzania: Ujamaa and rural development in the United Republic of Tanzania.

The Bottom Billion: Why the Poorest Countries are Failing and What Can Be Done About It (ISBN 0195311450), has been compared to Jeffrey Sachs's The End of Poverty and William Easterly's The White Man's Burden, two influential books, which like Collier's book, discuss the pros and cons of developmental aid to developing countries.

His 2010 book The Plundered Planet is encapsulated in his formulas: Nature - Technology + Regulation = Starvation, Nature + Technology - Regulation = Plunder, and Nature + Technology + Regulation (Good Governance) = Prosperity. The book describes itself as an attempt at a middle way between the extremism of "Ostriches" (Denialism, particularly climate change denial) and "Environmental Romanticism" (for example, anti-genetically modified organisms movements in Europe). The book is about sustainable management in relation with the geo-politics of global warming, with an attempt to avoid a global tragedy of the commons, with prime example of overfishing. In it he builds upon a legacy of the economic psychology of greed and fear, from early Utilitarianism (Jeremy Bentham) to more recently the Stern Review.