In the first major revision of this work for some years, changes were overdue to both its form and content if we were to ensure its continuance as a valuable reference book for school and undergraduate work. While remaining within the tradition set by the previous authors, we provide more of the encyclopaedic type of entry, in particular for terms central to theory and for those describing a phenomenon or process central lo much else in the discipline. These articles and the extensive cross-referencing of most entries will not please everyone, least of all those who consult this dictionary merely as a lexicon. For brevity's sake we have dispensed with many definite and indefinite articles, but have tried to keep the result grammatical.