Modeling is an essential step in understanding plant root systems (Fitter 1991, 1996, 2002). e inherent diculties in measuring root system structure and function make modeling uniquely important for this eld of research. Traditionally, there has been a division between modeling root system shape (cf.,  Berntson 1996; Lynch and Nielsen 1996; Pagès 2002) and modeling of physiological processes carried out by plant roots (cf. Silberbush 1996, 2002; Sperry et al. 2002). In recent years, the tendency has shied toward combined structural-functional models. ese include an architectural element simulating the structural development of the root system with functional simulation of physiological and ecological processes at the root-soil interface. In this chapter, we review techniques used for modeling nutrient uptake and root-rhizosphere interactions. Later, we describe modeling of root system structure and function in 3D space using SimRoot as an example (Lynch et al. 1997). A brief account of future simulation needs concludes this chapter.