Abstract Among the many objections to Turkish membership of the European Union lie claims that Turkey will be a powerful actor in the future EU, with a population as large as or larger than Germany. Many also claim that this power will have negative effects on the EU. We examine such claims analytically, influenced strongly by spatial models of EU policy-making. We find that Turkey's preferences lie sufficiently outside the EU mainstream that it will have little influence in day-to-day policy-making under the assent, co-decision, consultation and co-operation procedures (or the common procedure in the Constitutional Treaty). Its influence may be more evident in areas such as the CFSP or JHA, where unanimity remains the normal procedure. Still, Turkey's veto power here is no different from that of other, much smaller countries. Furthermore, veto power can only block changes and cannot be used to pull the EU in undesirable new directions. Even this veto power can be avoided if the EU-27 establish whatever policies they desire prior to Turkish membership, forcing Turkey to accept a fait accompli. Despite these limitations to its power, Turkey may have some influence in purely intergovernmental settings such as negotiations over new treaties that might occur some decades hence.