The Boreal Shield Ecozone, as defined by the Commission for Environmental Cooperation (CEC), is the largest ecozone in Canada. Covering 1.8 million square kilometres it covers almost 20% of Canada's landmass, stretching from northern Saskatchewan to Newfoundland.

The retreat of the Laurentide Ice Sheet left a landscape of broadly rolling uplands and lowlands with precambrian granitic bedrock outcrops. Few clear drainage channels were left in the rocky sediments deposited by the glacier resulting in a deranged drainage pattern. The numerous wetlands and lakes formed give this ecozone a unique character. Water features in this ecozone contain 22% of Canada's freshwater surface area.

Soil types vary widely across the region in response to the wide range of climate and soil components present. Cryosols are found in the most northerly areas wherever there is permafrost. Accumulation of organic matter, particularly peat, results in organic soils in much of the area. Brunisols occur in the north and west of the region where coarse to medium sediments are found. In these soils, soil formation is ongoing and will eventually result in either podzols or luvisols. In the south and east, podzols are found under forests growing primarily on sand in cold conditions. Gleysols are found where poor drainage has resulted in depleted oxygen. Luvisols are present where forests overlay clay deposits. These two soil types occur across the region wherever these conditions occur.

This ecozone can be further subdivided into six ecoprovinces:

Each province continues to work on defining subregions within the larger national ecozone and ecoprovince system.

The Alberta Natural Subregion - Natural Regions (2006) found within this ecozone are:

The Manitoba Ecoregions within this ecozone are:

The Saskatchewan Ecoregions within this ecozone are: