One of the most important strategic issues for managers involves deciding the size of the organisation. Factors which influence this decision include economic, social and political change. The boundaries of the organisation are thus not fixed, and are in part contingent upon the particular characteristics of the environmental context. Theoretical progress in the discipline of strategic management, as far as it relates to matters of organisational size (and structure), requires that serious consideration be given to the analysis of the dynamics of vertical integration which is available in the New Institutional Economics literature. One of the most interesting strands in this literature is the Transactions Costs Economics developed by R.H. Coase and O.E. Williamson. This paper provides an overview of the Coase-Williamson theory of vertical integration. It then uses this theory as a point of departure in conducting an empirical discussion of decisions to integrate vertically taken by one of the world's largest mining enterprises, The Broken Hill Proprietary Company Limited, during the first 30 years of its existence. The paper seeks to demonstrate that theorising in strategic management is enriched if analytical (albeit critical) attention is paid to advances in the economics of organisation.