Defining Markets for Ex Ante Regulation using the Hypothetical Monopoly Test

The EU is gradually systematizing its approach to ex ante regulation (notably with the publication of the recent regulatory framework for Electronic communications). Market definition is viewed as an essential first step in this, with the 'Hypothetical Monopoly Test' a useful conceptual tool for use in the assessment. This paper examines the use of this test for market definition when there are several differentiated goods or services under consideration. It sets out an analytic framework, discusses the pros and cons of using the test and illustrates its use in a Telecom context.