We live in an age of science; and throughout this century in particular man has made extraordinary progress both in his understanding of the universe and in his use of scientific knowledge to improve the quality of life. All around us we find examples of its benefits: television, aeroplanes, new medicines to conquer disease, computers, synthetic materials for clothes and furnishings. There is of course a darker side. We may have reached the Moon and before long will have set foot on Mars: but at the same time we are steadily destroying Mother Earth. Material resources are being used up at an unprecedented rate; the tropical rain forests are disappearing — 50 hectares are being cut down every minute; acid rain is polluting the soil; we are pouring noxious substances into the atmosphere and thereby probably bringing about long-term and perhaps irreversible changes in the world’s climate. It would be quite wrong, however, to lay the blame wholly on scientists. The reasons for man’s predicament are numerous and broadly political, social, and economic. Indeed to a greater or lesser extent we must all accept our share of responsibility; and it is incumbent on each one of us to do what we can to reverse current trends if we have any concern at all for future generations. Moreover, it is not science as such which is on trial so much as the way we use it. So what then is science? What is the scientist trying to do? What are his methods? These seemingly straightforward questions do in fact lead to some quite complex philosophical problems.