The paper uses an original international database on regulation, market structure and performance in the telecommunications industry to investigate the effects of entry liberalisation and privatisation on productivity, prices and quality of service in long-distance (domestic and international) and mobile cellular telephony services in 23 OECD countries over the 1991-1997 period. The data on regulation and market structure is analysed by means of factor analysis techniques in order to group countries according to their policy and market environments. Controlling for technology developments and differences in economic structure, panel data estimates show that prospective competition (as proxied by the number of years remaining to liberalisation) and effective competition (as proxied by the share of new entrants or by the number of competitors) both bring about productivity and quality improvements and reduce the prices of all the telecommunications services considered in the analysis ...