Canada's boreal forest is a vast region comprising about one third of the circumpolar boreal forest that rings the Northern Hemisphere, mostly north of the 50th parallel. Other countries with boreal forest include Russia, which contains the majority; the United States in its northernmost state of Alaska; and the Scandinavian or Northern European countries (e.g. Sweden, Finland, Norway and small regions of Scotland). In Europe, the entire boreal forest is referred to as taiga, not just the northern fringe where it thins out near the tree line. The boreal region in Canada covers almost 60% of the country's land area. The Canadian boreal region spans the landscape from the most easterly part of the province of Newfoundland and Labrador to the border between the far northern Yukon and Alaska. The area is dominated by coniferous forests, particularly spruce, interspersed with vast wetlands, mostly bogs and fens. The boreal region of Canada includes eight ecozones. While the biodiversity of regions varies, each ecozone has characteristic native flora and fauna.

The boreal forest zone consists of closed-crown conifer forests with a conspicuous deciduous element (Ritchie 1987). The proportions of the dominant conifers (white and black spruces, jack pine (Pinus banksiana Lamb.), tamarack, and balsam fir) vary greatly in response to interactions among climate, topography, soil, fire, pests, and perhaps other factors.

The boreal region contains about 13% of Canada's population. With its sheer vastness and forest cover, the boreal makes an important contribution to the rural and aboriginal economies of Canada, primarily through resource industries, recreation, hunting, fishing and eco-tourism. Hundreds of cities and towns within its territory derive at least 20% of their economic activity from the forest, mainly from industries like forest products, mining, oil and gas and tourism. The boreal forest also plays an iconic role in Canada's history, economic and social development and the arts.

The Canadian boreal forest is a very large bio-region that extends in length from the Yukon-Alaska border right across the country to Newfoundland and Labrador. It is over 1,000 kilometres (620 mi) in width (north to south) separating the arctic tundra region from the various landscapes of southern Canada. The taiga growth (as defined in North America) along the northern flank of the boreal forest creates a transition to the tundra region at the northern tree line. On the southwestern flank, the boreal forest extends into sub-alpine and lower elevation areas of northern British Columbia. The central interior of the province is occupied by a sub-boreal transition zone between the main boreal forest and the dry forests of the southern interior. However, across the Prairie Provinces, a band of aspen parkland marks a different kind of transition along the south-central flank from boreal forest to grassland. In Central Canada, the southeastern flank is marked by the Eastern forest-boreal transition of Central Ontario and western Quebec. It consists mainly of mixed coniferous and broad-leaf woodlands. South of this transition can be found the deciduous woodlands of Southern Ontario.

Canada's boreal forest is considered to be the largest intact forest on Earth, with around three million square kilometres still undisturbed by roads, cities and industrial development. Its high level of intactness has made the forest a particular focus of environmentalists and conservation scientists who view the untouched regions of the forest as an opportunity for large-scale conservation that would otherwise be impractical in other parts of the world.

The Canadian boreal forest in its current form began to emerge with the end of the last Ice Age. With the retreat of the Wisconsin Ice Sheet 10,000 years ago, spruce and northern pine migrated northward and were followed thousands of years later by fir and birch. About 5,000 years ago, the Canadian boreal began to resemble what it is today in terms of species composition and biodiversity. This type of coniferous forest vegetation is spread across the Northern Hemisphere. These forests contain three structural types: forest tundra in the north, open lichen woodland further south, and closed forest in more southern areas. White spruce, black spruce and tamarack are most prevalent in the four northern eco-zones of the Taiga and Hudson Plains, while spruce, balsam fir, jack pine, white birch and trembling aspen are most common in the lower boreal regions. Large populations of trembling aspen and willow are found in the southernmost parts of the Boreal Plains.

One dominant characteristic of the boreal is that much of it consists of large, even-aged stands, a uniformity that owes to a cycle of natural disturbances like forest fires, or outbreaks of pine beetle or spruce budworm that kill large tracts of forest with cyclical regularity. For example, the many stands of white spruce, black spruce, and balsam fir are vulnerable to the cyclical outbreaks of a species of the spruce budworm, the Choristoneura fumiferana. Since the melting of the great ice sheet, the boreal forest has been through many cycles of natural death through fire, insect outbreaks and disease, followed by regeneration. Prior to European colonization of Canada and the application of modern firefighting equipment and techniques, the natural burn/regeneration cycle was less than 75 to 100 years, and it still is in many areas.

Terms like old growth and ancient forest have a different connotation in the boreal context than they do when used to describe mature coastal rain forests with longer-lived species and different natural disturbance cycles. However, the effects of forest fires and insect outbreaks differ from the effects of logging, so they should not be treated as equivalent in their ecological consequences. Logging, for example, requires road networks with their negative impacts, and it removes nutrients from the site, which may deplete nutrients for the next cycle of forest growth. Fire, on the other hand, recycles nutrients on location (except for some nitrogen), it removes accumulated organic matter and it stimulates reproduction of fire-dependent species.