The hymenopteran family Ichneumonidae comprises one of the largest single animal families. With around 2,300 British species, almost 10% of British insect species are ichneumonids. They can be found everywhere and studying them is very rewarding, but it is not without its difficulties. This book provides an extensively illustrated key for the identification of the 35 subfamilies of Ichneumonidae known to occur in Britain and Ireland (plus Brachycyrtinae, not yet found here). This is supported by chapters for each subfamily giving a comprehensive review of current knowledge on systematics, biology and host relations together with notes on useful recognition features and references to the most relevant species-level identification literature concerning the British Isles. Included in each British and Irish subfamily account is a folio of photographs covering all recognised tribes.