Evidence provided in this monograph supports the conclusion that the genera Atrichornis and Menura are sufficiently distinct for each to be placed in a monotypic family, viz. the Atrichornithidae and the Menuridae. The suborder Menurae, in which these two families are usually placed, should be merged with the suborder Oscines of the Passeriformes as the differences between them are not sufficiently large to justify continued recognition of these two suborders. The Atrichornithidae and the Menuridae are each other's closest relatives, but the evidence available in this monograph does not suggest an especially close relationship to the Ptilonorhynchidae. It is recommended that the Atrichornithidae and the Menuridae be placed in a superfamily, the Menuroidea, of unknown affinities within the Oscines. The Menuroidea do not appear to be primitive within the Oscines. They are not closely related phylogenetically to the Rhinocryptidae of the Tyranni. Reduction in flying ability of the Menuroidea is presumably advanced in the Oscines and is reflected in a number of morphological features of the skeletomuscular system. The extreme terrestrial habits of the species of the Menuroidea, together with the long incubation and fledgling periods of the single annual chick (two in A. rufescens) , may be contributing to their decline. Moreover, the scrub-birds and lyrebirds may be relict remnants of an earlier larger radiation, and are unable to compete successfully with other avian species and/or to cope with recent changes in the environment, such as the introduction of foxes and feral cats. Conservation efforts for the scrub-birds and lyrebirds should consider the morphological and systematic findings presented in this monograph in addition to ecological data, with the suggestion that the undertakings for the Two Peoples Bay population of Atrichornis clamosus serve as a model for future actions.