This report provides an overview of the economic impact of ICT on economic performance, and the ways through which it can be measured. Using available OECD data, the first part of the book examines the available measures of ICT diffusion, the role and impact of ICT investment and the role of ICT-using and ICT-producing sectors in overall economic performance. The second part of the book offers nine studies for OECD countries, based on detailed firm-level data and prepared by researchers and statisticians from a wide range of OECD countries. These studies use a variety of methods and provide detailed insights on the effects of ICT in individual countries.