The Atlas Mountains divide the country into two regions, the well-watered north and the semi-arid south. The northern region, which contains the Kroumirie Forest, Bizerte, and the Medjerda River Valley, is further divided into three subregions: the northwest, with extensive cork forests; the north central, with its fertile grasslands, and the northeast from Tunis to Cap Bon, noted for its livestock, citrus fruits and garden produce.

The southern regions contains a central plateau and a desert area in the extreme south, which merges into the Sahara and is characterised by the date palm oases and saline lakes. The Medjerda Mountains, which run from Kroumirie to Bizerte, and the Tébessa Mountains (or Massif Meridional), in the southern region, are the two most important mountain ranges. The Medjerda, the most important river system, rises in Algeria and drains into the Gulf of Tunis.