When I was invited to take part in this Conference it was suggested that I should speak on some aspects of the population problem in relation to poverty, social inefficiency and mental disorder, as illustrated by the Merseyside Survey. At first I confess I felt very hesitant about it, for I did not want to go over ground that might already be familiar to you. But then I reflected that the purpose of the Conference was, no doubt, to recall and discuss work done in the past having some bearing on the quality of the population—an aspect of the problem that is only beginning to receive the attention it deserves. Before replying I therefore consulted Dr. Blacker as to whether it might meet your purpose if I attempted to summarize quite simply a few of the conclusions reached in the course of the Merseyside Survey concerning certain subnormal types in the community. It was only after I had been fortified by his reassurance and that of Dr. Cook that I ventured to accept your kind invitation, and I make my apologies here and now to any of you who find it tedious to listen to a reproduction of what you may have read in the published account of the Survey.