May 1995 How does an economy's efficiency in financial transactions affect its efficiency in physical production? And how does the volume of financial transactions relate to the level of real activity? There is a close, if imperfect, relationship between the effectiveness of an economy's capital markets and its level (or rate of growth) of real development. This may be because financial markets provide liquidity, promote the sharing of information, or permit agents to specialize. There is literature about how these functions help increase real activity, but surprisingly little literature predicting how the volume of activity in financial markets relates to the level or efficiency of an economy's productive activity. Bencivenga, Smith, and Starr address this question: How does the efficiency of an economy's equity market -- as measured by transaction costs -- affect its efficiency in producing physical capital and, through this channel, final goods and services? The answer: As the efficiency of an economy's capital markets increases (that is, as the transaction costs fall), the general effect is to cause agents to make longer-term -- hence, more transaction-intensive -- investments. The result is a higher rate of return on savings and a change in its composition. These general equilibrium effects on the composition of savings cause agents to hold more of their wealth in the form of existing equity claims and to invest less in the initiation of new capital investments. As a result, a reduction in transaction costs can cause the capital stock either to rise or fall (under scenarios described in the paper). Further, a reduction in transaction costs will typically alter the composition of savings and investment, and any analysis of the consequences of such changes must take those effects into account. This paper -- a product of the Finance and Private Sector Development Division, Policy Research Department -- was prepared for a World Bank Conference on Stock Markets, Corporate Finance, and Economic Growth. The study was funded by the Bank's Research Support Budget under the research project Stock Market Development and Financial Intermediary Growth (RPO 679-53).