It was a compliment to me to be asked to prepare the fourth edition of Westcott's Plant Disease Handbook, and the decision to accept the respon­ sibility for the fourth edition, the fifth edition, and now the sixth edition was not taken lightly. The task has been a formidable one. I have always had great respect professionally for Dr. Cynthia Westcott. That respect has grown considerably with the completion of the three editions. I now fully realize the tremendous amount of effort expended by Dr. Westcott in de­ veloping the Handbook. A book such as this is never finished, since one is never sure that everything has been included that should be. I would quote and endorse the words of Dr. Westcott in her preface to the first edition: "It is easy enough to start a book on plant disease. It is impossible to finish it. . . " This revision of the Handbook retains the same general format contained in the previous editions. The chemieals and pesticides regulations have been updated, major taxonomie changes have been made in the bacteria, fungi, nematodes and viruses, the changing pieture in diseases caused by viruses and/ or viruslike agents have been described. New host plants have been added, and many recently reported diseases as weIl as previously known diseases listed now on new hosts have been included.