"Might the dollar eventually follow the precedent of the pound and cede its status as leadinginternational reserve currency? Unlike ten years ago, there now exists a credible competitor: theeuro. This paper econometrically estimates determinants of the shares of major currencies in thereserve holdings of the world's central banks. Significant factors include: size of the home country,inflation rate (or lagged depreciation trend), exchange rate variability, and size of the relevant homefinancial center (as measured by the turnover in its foreign exchange market). We have not foundthat net international debt position is an important determinant. Network externality theories wouldpredict a tipping phenomenon. Indeed we find that the relationship between currency shares andtheir determinants is nonlinear (which we try to capture with a logistic function, or else with adummy “leader” variable for the largest country). But changes are felt only with a long lag (weestimate a weight on the preceding year's currency share around .9). The advent of the eurointerrupts the continuity of the historical data set. So we estimate parameters on pre-1999 data, andthen use them to forecast the EMU era. The equation correctly predicts a (small) narrowing in thegap between the dollar and euro over the period 1999-2004. Whether the euro might in the futurerival or surpass the dollar as the world's leading international reserve currency appears to depend ontwo things: (1) do the United Kingdom and enough other EU members join euroland so that itbecomes larger than the US economy, and (2) does US macroeconomic policy eventually undermineconfidence in the value of the dollar, in the form of inflation and depreciation. What we learn aboutfunctional form and parameter values helps us forecast, contingent on these two developments, howquickly the euro might rise to challenge the dollar. Under two important scenarios the remainingEU members, including the UK, join EMU by 2020 or else the recent depreciation trend of the dollarpersists into the future the euro may surpass the dollar as leading international reserve currencyby 2022"--National Bureau of Economic Research web site.