The world's largest biome is the taiga or the northern coniferous forest
A biome is an naturally occurring community of plants and animals that occupy a large distinct region and are adapted to that region.
Biomes on land around the world
By Ville Koistinen (user Vzb83) - the blank world map in Commons and WSOY Iso karttakirja for the information, CC BY-SA 3.0, Link
The taiga is marked with dark green. Most of Canada, Siberia, Scandinavia+Finland and Northern European Russia is part of the taiga. If you want to see how it looks like, read this blog and check out the photos taken in the suburbs. Out of all forested land in the world, the taiga comprises nearly a third.