The IESO is a non-profit, regulated corporation without share capital. It is regulated by the Ontario Energy Board (OEB), and its directors are appointed by the Ontario government.

The IESO has two distinct roles:

1. Ensuring the reliability of the integrated power system

The IESO and all market participants are jointly responsible for ensuring the reliability of the power system. From its system control centre, the IESO manages the production and flow of electricity to local distribution utilities and major wholesale customers in Ontario, while adhering to all appropriate operating and reliability standards. The IESO gathers real-time information on voltage levels, power flows, and equipment status. Trained and certified IESO staff monitor this information and manage the security and adequacy of the power system 24 hours a day, every day of the year. The IESO also forecasts short and long term supply requirements, encouraging power industry investment in the province. It will advise government if additional steps are needed to ensure adequate and reliable supplies of electricity in the future.

2. Overseeing the IESO-administered wholesale markets

The IESO administers a set of rules (the Market Rules) that govern the operation of the wholesale electricity market. The IESO monitors and analyzes market activity to ensure compliance with these rules and fair market competition. The IESO itself does not buy or sell electricity. It administers the wholesale electricity market by authorizing market participants, publishing system forecasts and market information, producing invoices, and performing financial settlement transactions for the markets.