"This book provides an introduction to human cytogenetics. It is also suitable for use as a text in a general cytogenetics course, since the basic features of chromosome structure and behavior are shared by all eukary­ otes. Because my own background includes plant and animal cytogenet­ ics, many of the examples are taken from organisms other than the human. Since the book is written from a cytogeneticist's point of view, human syndromes are described only as illustrations of the effects of abnormal chromosome constitutions on the phenotype. The selection of the phenomena to be discussed and of the photographs to illustrate them is, in many cases, subjective and arbitrary and is naturally influenced by my interests and the work done in our laboratory. " The above paragraph from the Preface of the first edition of this book also fits the present edition. However, so much has happened in five years in cytogenetics that-apart from a couple of pages here and there-the whole book has been rewritten and nine new chapters have been added. The system used in the first edition to cite, whenever possible, the latest and/or the most comprehensive review rather than the original publica­ tions has been followed here also. Not only would complete literature citations increase the size of the book too much, but many readers have expressed satisfaction with the referencing method used here.