Wikipedia has articles relating to two separate ecoregion classification systems:

• Ecoregions defined by the Commission for Environmental Cooperation (CEC) and partner agencies in Canada, Mexico, and the United States:
  • List of ecoregions in North America (CEC)
  • List of ecoregions in the United States (EPA)
• Ecoregions of the world defined by the conservation group World Wildlife Fund (WWF) :
  • Global 200 ecoregions (WWF), 238 single or combined ecoregions identified by the World Wildlife Fund (WWF) as priorities for conservation.
  • List of terrestrial ecoregions (WWF) 867 terrestrial ecoregions.
  • List of marine ecoregions (WWF), 232 marine ecoregions of the coastal and continental shelf areas.
  • List of freshwater ecoregions (WWF), 426 freshwater ecoregions.
  • Lists of ecoregions by country