The genus Leioproctus Smith embraces a major group of bees in Australia. The limits of this group have not been clearly understood. Michener (1965) considered Leioproctus to be highly variable and recognised the genus by a complex of characters, not one of which was invariable. He divided the genus in Australia into 20 subgenera, many of which were known by few specimens or only one sex. This revision has considered Australian bees of Leioproctus at species level. As a result, Michener's subgenera Chrysocolletes and Goniocolletes are both considered genera and his subgenus Microcolletes is synonymised with Protomorpha. In addition, 8 new subgenera are established (Zosterocolletes, Alokocolletes, Exleycolletes, Hadrocolletes, Charicolletes, Minycolletes, Rhabdocolletes, and Tanycolletes). In the subgenus Leioproctus 7 species-groups are recognised. Keys and line drawings that enable the classification of Australian genera, subgenera, species-groups and species are provided. Distribution maps for each species are given. Internal anatomy of Leioproctus is described and illustrated for the first time. Biological information that incorporates new and previously reported records and observations is presented. Twenty-seven new species are described: Leioproctus (L.) guadrimaculatus; L. (L.) crinitus; L. (L.) litotes; L. (Alokocolletes) seguax; L. (Odontocolletes) asper; L. (Odontocolletes) pachyodontoides; L. ( Ceratocolletes) xanthosus; L. ( Charicolletes) cardaleae; L. (Charicolletes) exleyae; L. (Minycolletes) vegrandis; L. (Minycolletes) paulus; L. (Minycolletes) pissinus; L. (Minycolletes) ceterus; L. (Minycolletes) exiguus; L. (Minycolletes) aguilus; L. (Rhabdocolletes) palapes; L. (Rhabdocolletes) pyrrhogaster; Chiysocolletes pilosus; Ouysocolletes enigma; Goniocolletes anthedonus; G. badius; G. ciliata; G. ciliata; G. comatus; G. dasypus; G. parvus; G. rugosus. The following synonyms have been recognised - Andrena advena Smith, 1862 = [Paracolletes euphenax Cockerell, 1913b; Paracolletes scitulus Cockerell, 1921; Paracolletes advena phillipensis Rayment, 1953] ; Andrena chalybeatus Erichson, 1842 = [Leioproctus vigilans Smith, 1879; Paracolletes diodontus Cockerell, 1929c; Nodocolletes dentatus Rayment, 1931; Nodocolletes subdentatus Rayment, 1931]; …………………………………