The mildew problem is discussed in popularised form and in the light of modem knowledge concerning the mould fungi, especially their conditions of growth. The various effects of mildew action on cotton goods are also reviewed and reference is made to a number of cases which have been investigated, describing the organisms which have been isolated. On measures for the prevention of mildew, it is shown that the present knowledge of the efficiency of antiseptics in size is quite unsatisfactory and that more is to be hoped, at present, from methods of sanitation and better conditions of packing and storage.