Hayek worked out a systematic explanation of the emergence and dynamics of informal social rules that accounts for the social rules and institutions we see in terms of deeper levels not obvious to the casual observer. The explanation relies on three fundamental ideas: the idea of a rule (and rule-following), of spontaneous order and of evolution. These ideas are interdependent parts of a single, integrated explanatory scheme, intended to show ordered elements of social life are not the product of design, but rather are the unintended consequences of impersonal and external forces operating on behavior and thought of human beings. Hayek’s theory of social evolution offers an explanation of the emergence and establishment of social rules in a group. To do this he must explain: (i) how it is that rules emerge; which (ii) are social rules; and (iii) the same rules across individuals; which (iv) then spread through the group as a whole. It is argued that he fails in the second and third of these tasks.