In this paper, I attempt to bring into focus what I believe to be some of the important practical issues that face development planners in the field of project appraisal. I shall try, insofar as possible, to recognize the handicaps under which planners operate, most importantly the handicaps imposed by imperfect foresight and by the virtual necessity of decentralized decision-making. To elaborate briefly on these handicaps, I think we must take it for granted that our estimates of future costs and benefits (particularly the latter) are inevitably subject to a fairly wide margin of error, in the face of which it makes little sense to focus on subtleties aimed at discriminating accurately between investments that might have an expected yield of 101/2 percent and those that would yield only 10 percent per annum. As the first order of business we want to be able to distinguish the 10 percent investments from those yielding 5 or 15 percent, while looking forward hopefully to the day when we have so well solved the many problems of project evaluation that we can seriously face up to trying to distinguish 10 percent yields from those of 9 or 11 percent.