Though it is not yet ten years since the last edition of British Ascomycetes was compiled, research on these fungi in Europe and North America has been so active that its text is already in part obsolete and has had to be extensively rewritten. The introductory matter has been curtailed, since it is assumed no one would purchase a work so entitled unless he already had a basic familiarity with the group. The section on taxonomy and nomenclature has been omitted as the topic is more fully treated in other works now readily available to students. There have unfortunately been many inevitable changes in familiar generic names but the reader who finds these exasperating should remember they are largely due to thoroughly bad work by nineteenth century authors who freely adopted generic names without troubling to enquire if they had already been used by earlier botanists in a different sense. Even so the process of eliminating invalid names is far from complete though I have resisted the overthrow of important old-established names like Durella, Rutstroemia, Sclerotinia and Sepultaria, all of which are threatened if a sense of responsibility and desire for stability does not blunt the enthusiasm of nomenclatorial pedantry. Apart from these sterile exercises there has been extensive taxonomic revision, especially in the Loculoascomycetes, to bring the text more into line with modem concepts. All the species figured in the last edition have been retained but some plates have been redrawn and new blocks prepared. These and all the line drawings now illustrate 77 species and 36 genera additional to those in the 1968 edition. Even so there remain many species known in Europe which are likely to occur in Britain and passing reference is made in the text to several of these in the hope that intensified collecting will bring them to light. Such completely unexpected recent discoveries in England as Caloscypha fulgens and Paurocotylis pita show how inadequately explored the British Ascomycete flora has been.