The new scheme of classification presented in this paper is based on the examination of all species in the family Thelypteridaceae which I have been able to trace in the Old World. I have gradually compiled a list of about 700 names (basionyms) and have examined type or other authentic material of all but a small proportion; and in the course of study of specimens in many herbaria I have noted about another 50 species which appear to be undescribed. I have attempted to re-describe all the previously-named species, noting characters not mentioned in existing descriptions, especially the detailed distribution of hairs and glands, including those on the body and stalk of sporangia, and characters of spores. It is probable that there remain some published names, not yet detected by me, which refer to species of the family, but I think there are not many. I have also made a study of all generic and infrageneric names which are typifiable by species of Thelypteridaceae, and in doubtful cases I have tried to clarify and fix the typification. As already reported in the second paper of this series (Blumea 18: 195—215), I have had the help of Dr. U. Sen and Miss N. Mittra in examining anatomical and other microscopic characters of some type species, and hope to present further information of this kind later.