This monograph arises out of a survey of the earthworm fauna of New Zealand soils, undertaken by the author in 1949 and completed in 1955, as a research project of the New Zealand Soil Bureau. The original aim of the project was to attempt to relate the distribution of the various soil groups of New Zealand and to evaluate their contribution to soil forming processes. Comprehensive collecting of specimens, followed by identification, revealed many new species of endemic Megascolecidae, and the systematic description of these species, together with a re-examination of type and named material of previously described species, has resulted in a re-appraisal of the taxonomy of the family and led to some revision of the classification.