This work, based upon the two Manchester Special Lectures given by the author in 1989-90, and focusing on the central economic issues of co-ordination and change, treats these as problems of equilibrium in the case of co-ordination and as problems of evolution in the case of change. The author explores the relationship between the two concepts of equilibrium and evolution and also examines the relationship between these conceptual ideas and the problems of change and co-ordination to which they apply. He extends his analysis to the behaviour of economic agents and the professional economists who attempt to explain the behaviour of economic agents, deciding to treat them on equal terms as two groups of scientists. Parallels are drawn with the work of the economist Stan Metcalfe (on technology strategy and the selection environment).