Investment in network infrastructure can boost long-term economic growth in OECD countries. Moreover, infrastructure investment can have a positive effect on growth that goes beyond the effect of the capital stock because of economies of scale, the existence of network externalities and competition enhancing effects. This paper, which is part of a project examining the links between infrastructure and growth and the role of public policies, reports the results on the links with growth from a variety of econometric approaches. Time-series results reveal a positive impact of infrastructure investment on growth. They also show that this effect varies across countries and sectors and over time. In some cases, these results reveal evidence of possible over-investment, which may be related to inefficient use of infrastructure. Bayesian model averaging of cross-section growth regressions confirm that infrastructure investment in telecommunications and the electricity sectors has a robust positive effect on long-term growth (but not in railways and road networks). Furthermore, this effect is highly nonlinear as the impact is stronger if the physical stock is lower.