Temperature is one of the major external inputs plants are exposed to from germination to senescence. Temperature variation has a strong inuence on the establishment and function of plant root systems; furthermore, temperature can aect overall plant productivity. In the rst edition of this book, Bowen (1991) covered the relationships of low and/or high temperatures on specic plant functions ranging from nutrient uptake and utilization to photosynthesis and carbon partitioning. In the second and third versions of this book, McMichael and Burke (1996, 2002) focused on optimal temperature for root growth, genetic diversity in the responses of plant roots to temperature, temperature stresses encountered in soil environments, changes in root metabolic activity, ultimate crop yields, and mycorrhizal associations. In this chapter, we update those topics as well as include root response to temperature gradients within the soil and particularly add a summary of the available noninvasive methods for studying temperature eects on root system development and function.