Although one of the earliest of biological disciplines, plant taxonomy remains an important and relevant aspect of modern botany. A disproportionate emphasis on the practice of plant taxonomy has to some extent caused the science to be seen solely as the activity of plant identification. This book attempts to redress the balance by providing an introduction to the taxonomic theory upon which the identification procedure is based. The second edition has been completely revised and updated by the author and edited by Norman Robson to reflect the rapid advances which have occurred in plant taxonomy since publication of the first edition.