The climate of five regions of the world is characterised by a regular period of winter rainfall followed by a summer drought of varying length. Such a climate is termed ‘mediterranean’ because it is the typical climate of most countries of the Mediterranean Basin. This climatic feature is also characteristic of four other regions of the world–namely: extensive areas of California, Chile, South Africa and southern Australia.

A biological invasion of any region is basically a process rather than an event and thus, to quote Deacon in his chapter in this section, ‘it is not restricted in time’. But for the reader to better understand the biogeographic aspects of invasions, the five chapters in this section provide some historical background to the biota of the five regions of mediterranean climate, especially as that background relates to human settlement of the regions.