The problems connected with the material used in the construction of aircraft are very numerous, and the time available in one lecture is far too short to consider them in any kind of detail. It seems to be more appropriate to approach the matter broadly and to consider some of the basic problems with a little thoroughness than to examine a number of details in a superficial manner. The main objection that can be urged against this method is that the conclusions reached are by no means confined in their application to aircraft materials, but apply almost equally to most of the arts in which the same or similar materials are employed. After all, the aeronautical engineer is mostly concerned to obtain the ideal sample of any chosen material.