Many writers have attached considerable importance to the idea that there is an optimum size for cities. A cursory examination of these writings soon reveals that most represent little more than strongly held opinions. Very few individuals writing on the subiect have attempted to demonstrate the strength of their convictions. With an emphasis on the more quantitative aspects of the subject, this study undertakes an examination of the optimum size concept with specific attention to the criterion of municipal efficiency and the implications that it has within the institutional context of Great Britain. The analysis in the study is in part theoretical and in part empirical. The theoretical portion is carried out in general terms so that it could have application within almost any national institutional context. However, the empirical analysis is restricted to selected local authorities in Great Britain.