Strigolactones (SLs), which are biosynthesized mainly in roots, modulate various aspects of plant growth and development. Here, we review recent research on the role of SLs and their cross-regulation with auxin, cytokinin, and ethylene in the modulation of root growth and development. Under nutrient-sufficient conditions, SLs regulate the elongation of primary roots and inhibit adventitious root formation in eudicot plants. SLs promote the elongation of seminal roots and increase the number of adventitious roots in grass plants in the short term, while inhibiting lateral root development in both grass and eudicot plants. The effects of SLs on the elongation of root hairs are variable and depend on plant species, growth conditions, and SL concentration. Nitrogen or phosphate deficiency induces the accumulation of endogenous SLs, modulates root growth and development. Genetic analyses indicate cross-regulation of SLs with auxin, cytokinin, and ethylene in regulation of root growth and development. We discuss the implications of these studies and consider their potential for exploiting the components of SL signaling for the design of crop plants with more efficient soil-resource utilization.