Infrastructure performs a vital role for the functioning of the economy. However, investments in the past have sometimes been wasteful. This chapter first assesses the impact of investment in energy, water, transport and telecommunication networks on the economy, showing that it has had effects on output over and above those of other types of investment. However, this relationship does not hold for all countries and types of infrastructure, and may have become weaker more recently. Policies that support a competitive environment, bolstered by greater independence of regulators and transparent decision making, determinies whether public or private investment is more appropriate. Such policies help to ensure more efficient investment in infrastructure.