© 2014 by John Wiley & Sons, Inc. This chapter reviews the organization and function of the plant root in relation to a variety of abiotic stress responses. It briefly defines the tissue organization of the root and highlights tissue-specific functions, signaling, and developmental pathways that are relevant to root stress responses. Next, the chapter summarizes recent progress in resolving root-associated stress response networks. It discusses how these networks give rise to phenotypic plasticity of the root system. The chapter then speculates on strategies to manipulate these stress response networks for crop improvement. It focuses on tissue-specific responses to nitrogen and salinity as two examples that illustrate root stress responses involved in (1) increasing foraging and uptake of a limited resource, and (2) excluding and avoiding a substance that is toxic at high levels. For each stress condition, root-associated responses are first reviewed and then recent advances in constructing root-associated response networks are highlighted.