The major developments in thought regarding regional economic growth and development are traced over the last two decades. The supply-side micro-foundations of regional growth have come under scrutiny in a manner which has previously not been evident. In particular, an examination of the elements of industrial clustering, regional industrial structure, and place characteristics which may promote innovation, have become a central focus of modern regional growth analysis. The micro-foundations of these arguments are analysed, and the links between innovation and clustering explored within a transactions-costs framework. This allows us to point to areas in which our understanding has grown over recent years, and to identify further areas of analysis which are required.