This volume is derived from a symposium on ‘The importance of being small: does size matter in biogeography?’ organised during the first BioSyst meeting, which was held in Leiden in August 2009. The idea for the symposium arose during an informal discussion at the Natural History Museum in London. Biogeography is now a well-established science with its own methods and tools, and a strong theoretical framework. Many journals and books are dedicated to biogeography, and specific meetings are organised by the International Biogeography Society. Nevertheless, most of the ideas in biogeography come from empirical evidence from macroscopic organisms, whereas the spatial patterns of microscopic organisms have mostly been neglected.

The aim of this book is to establish the importance of microorganisms in biogeography. In doing so, this book follows the stimulating discussion on the so-called ‘Everything is everywhere’ hypothesis of the last decades. Currently, enough empirical evidence is available on the biogeography and phylogeography of many microscopic organisms and on larger organisms with microscopic dispersing stages; thus, this book brings together for the first time all this information in a unifying framework, and discusses patterns, processes and consequences.

The coverage of the taxa is broad, spanning from prokaryotes to plants, fungi, and animals; the approaches are rather different in the different chapters, and I hope that readers will enjoy this book and find many inspirations for their own research.