The 18th century Irish economist, Richard Cantillon, made lasting contributions to economics, in particular, to classical economics. This note elucidates his conception of the economy as three distinct, yet interdependent systems – (1) production, distribution and exchange, (2) money, interest and prices, and (3) international trade and finance. It is, indeed, striking to find such a comprehensive account of the mechanisms operating in an economy in a text nearly three centuries old. These insights regarding the working of an economy, although a pre-capitalist one, provide a distinct approach to studying today’s economic problems. This is the surplus approach of classical political economy, revived by Piero Sraffa in 1960.