The performance requirements of large electrical plant such as a.c. turbo-type generators vary a great deal, so that the question of standardization is very complicated. It is also difficult, because each manufacturer has built up designs and manufacturing experience over a period of many years. Standardization will, of necessity, introduce changes in both design and manufacture which naturally will not find ready acceptance unless they carry with them some advantages. The technical difficulties in obtaining standardization of designs are formidable, and would require a great deal of consideration. The effect of standardization on future developments is of great importance, and must be given close attention.The possibilities of complete unification of designs, an alternative of mechanical interchangeability, and the standardization of requirements, which is the first step in either of these directions, are considered in turn.The conclusions arrived at are that for both commercial and technical reasons complete unification of designs must be regarded as unpractical under present conditions, and it seems very doubtful whether the alternative of mechanical interchangeability would be feasible. In view of the complexity of the problem the close collaboration of all engineers concerned will be essential.