Genetic and genomic approaches in model organisms have advanced our understanding of root biology over the last decade. Recently, however, systems biology and modeling have emerged as important approaches, as our understanding of root regulatory pathways has become more complex and interpreting pathway outputs has become less intuitive. To relate root genotype to phenotype, we must move beyond the examination of interactions at the genetic network scale and employ multiscale modeling approaches to predict emergent properties at the tissue, organ, organism, and rhizosphere scales. Understanding the underlying biological mechanisms and the complex interplay between systems at these different scales requires an integrative approach. Here, we describe examples of such approaches and discuss the merits of developing models to span multiple scales, from network to population levels, and to address dynamic interactions between plants and their environment.Root architecture critically influences nutrient and water uptake efficiency and plays a central role in plant productivity (Lynch, 1995); selecting new crop varieties with improved root traits may produce a second Green Revolution (Lynch, 2007). Over the past several decades, reductionist approaches have pinpointed the individual genes or mechanisms that control root system architecture (for review, see Benfey et al., 2010). However, as our knowledge of biological systems has increased, researchers have realized that the underlying components (e.g. gene products, cells, tissues, and organs) function in highly complex, dynamic networks. The existence of emergent traits, robustness, and hierarchical organization of biological systems make them challenging to conventional reductionist experimental approaches (Bruggeman and Westerhoff, 2007). Understanding these properties requires studying the system rather than its individual components. Also, in contrast to the simple linear networks conveyed in textbooks, biological networks usually contain multiple branches, feedback and/or feed-forward loops, and other complex regulatory motifs. For example, most signal transduction pathways include negative feedback and/or positive feedforward loops to switch off or amplify a response pathway. Hence, logic alone often fails to predict the output from such pathways. Systems approaches often employ mathematical or computational models to simulate the behaviors of these nonlinear networks and predict emergent behaviors (for review, see Middleton et al., 2012). Robust biological systems also have compensatory mechanisms that come into play when a key gene is removed. For example, 65% of knockout lines for Arabidopsis (Arabidopsis thaliana) transcription factors in the root stele gene regulatory network (GRN) showed molecular phenotypes, but only 16% showed morphological phenotypes (Brady et al., 2011). Thus, in the robust stele GRN, the network architecture or genetic redundancy can buffer or canalize changes in gene expression. Hierarchy is inherent to all biological systems. At scal...