The aim of this study is to give a description and classification of the known final larval instars of the Ichneumonidae. Subfamilies, tribes and genera are described and keys given. So far as possible, every species known on larval characters is illustrated. These figures illustrate the classification to the level of genera, summarize generic characters and show the range of characters within a genus. Illustrations are deliberately used in preference to lengthy verbal descriptions of generic characters. However, outstanding characteristics of genera are indicated. Some reference is made to differences between species, particularly where marked differences are known. Knowledge of the adults of these insects is much in advance of that of the larvae. A classification scheme based on larval characters may be congruent or incongruent with one based on adult characters. The independence of larvae and adults makes a separate evolution of their characters possible. Selective factors acting on the legless larvae are different from those acting on the mobile adults. The classification scheme followed here is in general agreement with that of Townes's (1969, 1970a, 1970b, 1971) notable series of monographs on the adults, where the world genera are brought together, redescribed and compared. There is remarkable agreement between the resulting classification scheme of Townes and a classification scheme based on larval characters, but, of course, also some discrepancies. The discrepancies indicate places where the classification needs to be reexamined.
The sequence in which genera are listed follows that of Townes unless the larval characters indicate some other placing. Species are generally listed alphabetically. An alphabetical sequence of figures in the plates was not always possible when grouping figures on size.