In a taxonomic revision of the genus Blechnum of the Malesian region 20 taxa (17 species and 3 subspecies) are recognised. Much of the past confusion over names, especially of the Papua New Guinea taxa, has been the result of some species being based on inadequate, often single, collections. One new species and one new subspecies are described and two new combinations are made. Fortythree species and seven varieties are put into synonymy. A key, full descriptions, distribution maps and illustrations of the less well understood taxa, as well as scanning electron microscope images of the spores, are presented. Where a taxon also occurs outside the Malesian region, full distributional details are provided, so far as can at present be verified by field observations and herbarium collections. The distribution patterns of a number of the taxa appear to be closely related to their limited ecological tolerances. The biogeography of the genus in the Malesian region is discussed.