TITANIUM, with a melting point of 1,660 deg. C, higher than that of nickel or iron, a density little more than one‐half that of steel, and a corrosion resistance in certain environments superior to stainless steel, is evidently a metal of significance to aeronautics. In the last few years remarkable advances have been made in both the production technology and the basic physical metallurgy of the titanium alloys, and it would be fair to say that aeronautics generally has not exploited the possibilities of these alloys to the extent that might have been expected. This is in part due to economic factors, as titanium is still relatively expensive, and in part due to a lack of conviction in the relative advantages which the alloys can offer. It is obvious that as more titanium is brought into use in aeronautics, so the economic aspect will improve, and the more experience will designers and materials engineers generally gain in its utilization. The purpose of the present article is to survey some of the basic metallurgical considerations which enter into the development of the titanium alloys, and relate these to the specific engineering factors of interest in aeronautics. This will lead to a discussion of the ways in which the titanium alloys are being introduced into aircraft structures and engines. The subject is clearly a very large one to attempt in a single article, and many quite important topics have necessarily been abridged or omitted altogether. The references should, however, make it possible to follow up individual subjects in more detail.