The authors describe the construction of the monetary services indexes (MSIs) in detail and provide a road map of the St. Louis MSI database. The database contains the MSIs and their dual price indexes; quantities, user costs, and own-rates of return for the indexes’ components; the currency-equivalent (CE) monetary index suggested by Rotemberg, Driscoll, and Poterba (1995); heretofore unpublished second moments of the MSIs, which were suggested by Barnett and Serletis (1990) as useful measures of the amount of (statistical) aggregation error contained in the MSIs; and a measure of aggregate total expenditures on the services of monetary assets. In addition to these derived series, the database includes the computer programs used to construct the MSIs and related aggregates. To facilitate comparison with monetary aggregates published by the Federal Reserve Board, the MSIs and related data in the database are provided for the same groupings of monetary assets—M1, M2, M3, and L—as well as for other widely-used aggregates such as M1A (currency plus non-interest-bearing checkable deposits) and MZM (M2 less small time deposits). The indexes are provided at monthly, quarterly, and annual frequencies.