This report is on the theoretical and practical aspects of the significant market power in telecommunications. It is part of a series of ITU telecommunication studies analyzing economic aspects of telecommunications and carried out by ITU/BDT's Market, Economics and Finance Unit (MEF). This report also reflects the results of the discussions on telecommunication market analysis during the seminar on Economic Dynamics of Newly Liberalized Telecommunication Markets in CEE Countries and Baltic States, held in Vilnius, Lithuania, in October 2004.