Current knowledge of mycorrhizal diversity in arctic and alpine tundra is based mainly on static surveys of mycorrhizal associations of plant taxa and fruiting patterns of selected ectomycorrhizal fungal species in specific habitats. Within these limitations, it appears that: (1) non-mycorrhizal plants are widespread and predominate in certain plant communities; (2) typical arbuscular mycorrhizal associations are ubiquitous in low arctic and alpine areas but that the level of root colonization is highly variable; (3) root colonization by dark septate fungi is a common event but that their ecological significance is still unknown; (4) a large number of ectomycorrhizal fungal species are present as symbionts of a relatively few widely distributed shrubs and herbaceous plant taxa; (5) ericaceous plants with erieoid mycorrhizas dominate large arctic and alpine areas covered by heath communities. Physical environmental features strongly limit and shape species diversity in arctic and alpine tundra. Cold-dominated environments provide extreme conditions for the establishment and functioning of mycorrhizal associations. Therefore, such systems are simple models to address the ecology and evolution of mycorrhizal symbioses. Molecular methods to identify mycorrhizal fungi on plant roots will resolve questions related to the structure and dynamics of communities of mycorrhizal fungi in arctic and alpine tundra.