Thorough, well informed planning is essential to develop electricity systems and prepare them for increased shares of renewables. Long-term electricity planning is highly relevant in centrally managed power systems or where power generation and transmission require co-ordination across multiple jurisdictions. Good long-term electricity plans can help to optimise decision-making, especially amid rapid technological innovation that involves trade-offs over resource and risk allocation. Effective planning, however, depends on sound regulatory oversight, comprehensive institutional processes and timely data. This report from the International Renewable Energy Agency (IRENA) identifies useful regulatory practices for the era of rapidly improving renewable energy technologies. It draws key insights, particularly, from experiences with integrated resource planning (IRP) in South Africa and parts of the United States. Effective power system planning incorporates stakeholder consultation and aligns with broader public policy goals. This helps to manage risks and encourages timely and efficient investment, the report finds.