The geographical area covered will be the whole of the geographical Europe. Each volume will illustrate the adults of all species in photographical colour plates of the best quality. Sexual dimorphism as well as polymorphism will be illustrated and if possible all subspecies too. Most species will be shown in natural size, but larger groups of small species such as the genera Idaea and Eupithecia will be shown enlarged. Each species will be treated using the following format: FULL NAME. ORIGINAL REFERENCE to all available nominal names (valid names and synonyms). DIAGNOSIS based on external features, including detail figures where necessary. MALE AND FEMALE GENITALIA of all species with line drawings or photographs. DISTRIBUTION. A summary of the European distribution and also of distribution outside the area treated.