A novel series of interest rates paid by the Corporation of London shows that interest rates in London declined by 350 basis points during the seventeenth century. The decline followed a similar pattern in Europe. Records from the Corporation’s archive provide evidence for financial development: an increase in the number and volume of debt instruments, an increase in the number of lenders, and the development of a secondary market. Econometric analysis establishes that increasing the debt instruments’ liquidity contributed to the convergence of interest rates between London and Amsterdam.