Today there is growing interest on the part of aeronautical engineers in forgings of large size, for three main reasons. Certain types of forgings will naturally need to be bigger as the aircraft itself becomes bigger; more composite structures are being replaced by single components made as forgings; and there is an increasing use of complex units machined directly from blocks of metal which are too big in at least one dimension to be made as extrusions or rolled plate. It is with these larger forgings that we are mainly concerned. Their production presents many serious problems. It is reasonable to hope that some of these will be overcome as experience grows and techniques are improved but others seem to be inherent in the materials used and must be appreciated at the design stage of the component if fully satisfactory service is to be obtained.