Five species of the nephilid genus Nephila Leach are found in the Australasian region, which for the purposes of this study was defined as Australia and its dependencies (including Lord Howe I., Norfolk I., Christmas I., Cocos (Keeling) Is), New Guinea (including Papua New Guinea and the Indonesian province of West Papua), Solomon Is, Vanuatu, New Caledonia, Fiji, Tonga, Niue, New Zealand and other parts of the south-west Pacific region. All species are redescribed and illustrated. Nephila pilipes (Fabricius) occurs in the closed forests of eastern and northern Australia, New Guinea, Solomon Is and Vanuatu (through to South-East Asia); N. plumipes (Latreille) is found in Australia (including Lord Howe I. and Norfolk I.), New Guinea, Vanuatu, Solomon Is and New Caledonia; N. tetragnathoides (Walckenaer) inhabits Fiji, Tonga and Niue; N. antipodiana (Walckenaer) occurs in northern Australia (as well as Christmas I.), New Guinea and Solomon Is (through to South-East Asia); and N. edulis (Labillardière) is found in Australia (including Cocos (Keeling) Is), New Guinea, New Zealand and New Caledonia. Epeira (Nephila) walckenaeri Doleschall, E. (N.) hasseltii Doleschall, N. maculata var. annulipes Thorell, N. maculata jalorensis Simon, N. maculata var. novae-guineae Strand, N. pictithorax Kulczyński, N. maculata var. flavornata Merian, N. pictithorax Kulczyński, N. maculata var. flavornata Merian, N. maculata piscatorum de Vis, and N. (N.) maculata var. lauterbachi Dahl are proposed as new synonyms of N. pilipes. Nephila imperialis var. novaemecklenburgiae Strand, N. ambigua Kulczyński, N. sarasinorum Merian and N. celebesiana Strand are proposed as new synonyms of N. antipodiana. Meta aerea Hogg, N. meridionalis Hogg, N. adelaidensis Hogg and N. meridionalis hermitis Hogg are proposed as new synonyms of N. edulis. Nephila picta Rainbow is removed from the synonymy of N. plumipes and treated as a synonym of N. edulis, and N. nigritarsis insulicola Pocock is removed from the synonymy of N. plumipes and treated as a synonym of N. antipodiana. Allozyme data demonstrate that N. pilipes is distinct at the 80% FD level from N. edulis, N. plumipes and N. tetragnathoides. Nephila plumipes and N. tetragnathoides, deemed to represent sister-taxa owing to the shared presence of a triangular protrusion of the male pedipalpal conductor, were found to differ at 15% FD in the genetic study. No genetic differentiation was found between 10 populations of N. edulis sampled across mainland Australia. Species of the genus Nephila have been extensively used in ecological and behavioural studies, and the biology of Nephila species in the Australasian region is extensively reviewed and compared with studies on Nephila species from other regions of the world.