We hear the expression “cost-benefit” a great deal nowadays; and when we do, we should always ask “cost to whom? Benefit to whom?” We should also remember that cost-benefit analysis requires that account be taken not only of financial gains and losses but also of all advantages and disadvantages of any kind. Consideration only of income and expenditure is investment appraisal, and many of the so-called “cost-benefit” studies of herbicide usage which have been published come into this category. Such studies are useful, but they should not be considered in isolation from investment appraisal of herbicide discovery, development, and production for the manufacturer; and both must be integrated into a total view of cost-benefit of weed control for the whole community, a broad and long-term view which takes account not only of economic values but also of social values. To make decisions and to formulate policies which will set herbicides in an optimum way in the social and economic context of an entire community and which will produce the most favourable cost-benefit for that whole community demands study and analysis of the total system. In the short time allocated to me I can do no more than skim over this wide field and indicate a number of relevant topics, and I plead guilty in advance to the charge of being superficial and of suggesting things that should be done without describing in detail how they could be done. My remarks will apply to the developed countries because the herbicide needs of the under-developed countries are a separate subject.