Popper first developed his theory of scientific method – falsificationism – in his The Logic of Scientific Discovery, then generalized it to form critical rationalism, which he subsequently applied to social and political problems in The Open Society and Its Enemies. All this can be regarded as constituting a major development of the 18th century Enlightenment programme of learning from scientific progress how to achieve social progress towards a better world. Falsificationism is, however, defective. It misrepresents the real, problematic aims of science. We need a new conception of scientific method, a meta-methodology which provides a framework for the improvement of the aims and methods of science as scientific knowledge improves. This aim-oriented empiricist idea can be generalized to form a conception of rationality – aim-oriented rationality – which helps us improve problematic aims and methods whatever we may be doing. In this way, Popper’s version of the Enlightenment programme can be much improved, indeed transformed.