For almost a century, the vast bulk of Ontario’s electricity was produced by Ontario Hydro and sold to consumers through local municipal utilities. As a first step toward a competitive market, the Ontario Electricity Act of 1998 re-organized Ontario Hydro into a number of successor companies including:

• Ontario Power Generation Inc. (OPG) - generates electricity and competes with other generating companies in the Ontario marketplace.
  
  
• Hydro One - transmits and distributes electricity across the province.
  
  
• The Independent Electricity System Operator (IESO) - is responsible for the safe and reliable operation of Ontario's bulk electrical system and also operates the wholesale marketplace.