The Wilbur Wright Lectures not only commemorate that pioneer flight on which the art of practical aviation was founded but also offer homage to the brilliant research and invention which made that flight possible. It is, therefore, natural and fitting that such a large proportion of the preceding 25 lectures have dealt specifically with the application of research to matters aeronautical. The materials of aeronautical construction can also justly be classed as the outcome of much research into many fields of pure and applied science, with practical results that have made some contribution towards the advancement of aviation and, hence, fittingly form the subject of a Wilbur Wright Lecture. Accordingly, when the Council of the Royal Aeronautical Society honoured me with the invitation to deliver the 1938 lecture on this subject, I naturally read up the preceding lectures and was somewhat surprised to find that materials, as such, had not previously been dealt with in this connection. The task of making the first survey of a field of such alarming scope, in a necessarily limited space and time, involved some anxious reflection regarding a suitable method of treatment; it appeared that a detailed discussion of personal research, or even of a selected group of materials, must have such a limited scope as to be incompatible with what is implied in the allotted title. To the casual observer, the really wide range of the more familiar materials of construction that have been available for some years, allied to the normal steady improvements that have been effected and those that may be expected, may appear to offer all that is required for the aeronautical requirements of the next decade or so, so that reviews of the materials of, say, 1924, 1931, 1938 and 1945 would mainly represent a story of development rather than change ; actually, this is not the position. A relatively few years has seen the relinquishment, temporary or permanent, of the position held by steel as a structural material; the use of light alloys has become very general, an improved form of wood is definitely in the field while it may be that the entire structure of moulded plastics will become a practical proposition in the fairly near future. Then, the accomplishment of the aims of the engine builder with regard to units of much greater powers are retarded to a certain extent by the fact that a number of materials appear to have reached the visible peak of their development; new materials are urgently required. Again, who would care to prophesy that the airscrew of the future 2,000-4,000 h.p. engine will even be made of any kind of metal, although the present aluminium alloy propellers give such good performance.