A Great deal of ink has been spilt during recent yearsonthe subject of the trend of the birth-rate and whether the population of this country will be maintained or will decline. Relatively little attention has, however, been paid to one of the factors that has a great deal to do with the course of births, viz. the supply of potential parents of both sexes. It is sometimes assumed that the position in this respect remains ‘normal’, whereas rather startling changes have occurred in recent years in the size of the reservoir of unmarried adults from which marriages are drawn, and it may be concluded from these that a considerable fall in the number of marriages, to be followed by a consequential fall in the number of births, is almost inevitable during the next few years.