PILAR NOGUES-MARCOThis article analyzes the stability of bimetallism for countries operating in integrated bullion markets that enact different legal ratios. I articulate a new theoretical framework to demonstrate that two countries can both be bimetallic only if they coordinate their legal ratios. The theoretical framework is applied to the mid-eighteenth century when London's legal ratio was 3.8 percent higher than that of Amsterdam. I find that Amsterdam was effectively on the bimetallic standard, whereas London was on a de facto gold standard.arly modern monetary policy is fascinating. It is also complex, involving interactions between mints, banks, and treasuries, and arbitrageurs in domestic and international markets. It is also understudied although eighteenth-century policies remain relevant today. In fact, the motivations of important actors and the market environment in which they operated are much less understood than their more familiar nineteenth-century counterparts. For instance, it is commonly believed that Sir Isaac Newton, Master of the Mint, mistakenly overvalued gold at the mint in 1717 (Jastram 1977, pp. 12-13; Cooper 1987, pp. 44-45; Kindleberger 1993, p. 60; Redish 1990, pp. 789-90; Eichengreen 1996, p. 12). What exactly is meant by this statement? What were the reasons for this "mistake," and what were its implications?This article reconstructs the relevant aspects of international monetary relationships during the eighteenth century. Doing so, helps us understand the operation of bullion markets during the eighteenth century