* Abstract - As the world becomes more globalized and resources become more internationally mobile, the issue of tax competition is moving to the forefront of debates surrounding national tax systems. Those who have studied taxation in a federal system of govern- ment will recognize that this debate is not new. This paper presents the conceptual issues that have arisen concerning tax competition in the fiscal federalism literature, and explores the reasons why the empirical measurement of the effects of tax competition, particularly corporate tax competition, is so difficult. Given the complicated nature of the problem and the theoreti- cal ambiguity on the consequences of tax competition, it should perhaps not be surprising for the empirical literature to find that competition sometimes increases and sometimes decreases tax rates.