The natural communities of the world are diverse, and many schools of ecology have developed classifications of communities in partial independence of one another. There is consequently a vast and widely dispersed literature on the classification of plant and animal communities, comprising divergent approaches of different schools and representing a great experiment on the usefulness of different possibilities for classification. The editor sought in a re view monograph of 1962 to summarize these schools and their history, and in 1973 published a treatise on 'Ordination and Clas sification of Communities' as volume 5 of the Handbook of Vegetation Science. We were fortunate, in preparing the latter work, to have a truly international panel of authors to discuss different major ap proaches to classification. This second edition of the book of 1973 is intended to make the work more widely available in a less expensive form as companion volumes on ordination and on classification of plant communities.