IEA Executive Director Maria van der Hoeven said in a statement the reliability and sustainability of future energy supplies depends on a high level of investment.
"But this won't materialize unless there are credible policy frameworks in place as well as stable access to long-term sources of finance," she said. "Neither of these conditions should be taken for granted."
She said there was a real risk that any investments in global energy could be misdirected because the environmental impacts of various resources may not be reflected in the overall costs.
The IEA's report says around 15 percent of annual investments target renewable energy resources, while the bulk of spending, more than $1 trillion, is directed at fossil fuels.
More than half of the energy supply investments are needed to keep production of oil and gas fields at current levels and to replace existing power plants before they reach the end of their life cycle.
IEA Chief Economist Fatih Birol said getting the investments in the right place require a level playing field.
"Policy makers face increasingly complex choices as they try to achieve progress towards energy security, competitiveness and environmental goals," he said. "These goals won't be achieved without mobilizing private investors and capital, but if governments change the rules of the game in unpredictable ways, it becomes very difficult for investors to play."