The only true desert to be found along the 0° meridian line also happens to be world's largest. The Sahara covers most of north Africa, more than a third of the continent, and an area around the same size as the United States. It is a desert of extraordinary variety. Temperatures in excess of 55° C have been recorded in parts of Libya, while in some places frost can be seen during the winter. All the standard desert landscape types are present in the Sahara, from great fields of shifting sand dunes or ergs, to vast plains filled with rocks, known as reg.

Rainfall in most parts of the Sahara is scant and erratic - some areas endure several years without even a hint of a shower. In common with other desert regions, storms in the Sahara can be extremely localised, often affecting an area as small as 20 square kilometres. Strong, unpredictable winds are typical of the Saharan weather systems, and these have come to be known by names such as khamsin, sirocco, shahali, and simoom. These winds can blow for days on end, bringing with them vast amounts of dust and sand, which cover everything in their path and reduce visibility close to zero. From time to time, particularly powerful sandstorms can be extremely unpleasant and dangerous for anyone caught in them. Dust devils, which are like whirlwinds, also occur, hurling sand, dust, small animals and plants into the air.

The Sahara is crossed by the Nile and Niger rivers, which together support most of the desert's human population. Even so, it still presents a great obstacle to animal and plant life. In later sections we consider some of the animals and plants which inhabit the Sahara, and we look at how they have adapted so that they can live there.