A CGD Policy Working Paper. The total scale of incremental investment requirements in infrastructure in developing countries has been estimated at around USD 1 trillion a year, with a range of related studies suggesting numbers between $815 billion to $1.3 trillion. While all such numbers are open to considerable debate, and were not designed to measure the cost of delivering the specific SDG infrastructure targets, they suggest the likely scale of the financing challenge for an SDG agenda which includes universal coverage to adequate housing, water, sanitation, modern energy and communications technologies. The complexity of infrastructure finance in developing countries suggests that external private investment will remain a minor player in the financing of infrastructure for development. Nonetheless, reforms of development finance institutions and multilateral development banks alongside infrastructure pricing in recipient countries could considerably increase financial flows, and the Addis Financing Conference later this year could help provide the authorizing environment for such reforms.