They are expected to increase in both scale and influence over the next decades due to greater wealth and the growing need to cater to ageing populations in both OECD and non-OECD countries. Institutional investors have traditionally provided long-term capital with investment portfolios built around the two main asset classes (bonds and equities) and an investment horizon tied to the often long-term nature of their liabilities (OECD, 2015g). Looking at large OECD pension funds only, direct investment in infrastructure projects of all types accounted for 1% of their asset allocation in 2013. Green infrastructure, including clean energy, is estimated to account for an even smaller share (ibid.). Too many barriers still stand in the way of scaling-up the participation of institutional investors (Box 2.2).