The paper examines the definition of foreign exchange reserves and related concepts. It also investigates to what extent the transparency and completeness of foreign exchange reserve data affected the course of financial crises in emerging market economies in the 1990 s. The author looks at how the practice of reserve data dissemination changed in the wake of these crises. Three case studies of crises in Mexico, Thailand and South Korea show that conventional measures of foreign exchange reserves provide a partial and sometimes misleading picture of economic conditions, Dąbrowski says. According to the author, this enables decision makers to postpone costly decisions and contributes to the risk of sudden reactions on financial markets. Financial crises have induced emerging market economies to substantially accumulate foreign exchange reserves and rearrange their policies on macroeconomic data dissemination by bringing them in line with IMF guidelines, the author argues. Under these guidelines, monetary authorities are required to publish data on gross reserves and on pre-determined and contingent net drains on foreign currency assets. This ensures a comprehensive picture of foreign currency liquidity and resilience to external shocks, Dąbrowski concludes.