The depth at which plants are able to grow roots has important implications for the whole ecosystem hydrological balance as well as for carbon and nutrient cycling. Here we summarize maximum rooting depth of species belonging to the major terrestrial biomes. We found 290 observations of maximum rooting depth in the literature which covered 255 woody and herbaceous species. Maximum rooting depth ranged from 0.3 m for some tundra species to 68 m for Boscia albitrunca in the central Kalahari; 196 species had roots at least 2 m deep 50 species had roots at a depth of 5 m or more and 22 species had roots as deep as 10 m or more. The average for the globe was 4.6 +0.5 m. Maximum root depth by biome was 2.0 m for boreal forest 2.1 m for cropland 9.5 m for desert 5.2 m for sclerophyllous shrubland and forest 3.9 m for temperate coniferous forest 2.9 m for temperate deciduous forest 2.6 m for temperate grassland 3.7 m for tropical deciduous forest 7.3 m for tropical evergreen forest 15.0 m for tropical grassland/savanna and 0.5 m for tundra. Grouping all species across biomes (except croplands) by three basic functional groups (trees shrubs and herbaceous plants) the average maximum rooting depth was 7.0 m for trees 5.1 m for shrubs and 2.6 m for herbaceous plants.