The root is one of the most important organs for plants. It not only anchors plants to the soil, but also functions as the main organ for taking up water and nutrients from the soil environment. Our comprehension of root development initially stemmed from studies using classical genetic approaches and has been greatly enhanced by the advancements in modern molecular biology and genomics techniques. Unlike other plant organs, we now have a comprehensive map of individual cell types in roots, at different developmental stages, and in response to various stimuli. Consequently, root research has ascended to the forefront of plant development biology. This chapter delves into the exploration of root development using Arabidopsis thaliana as a model system. In Arabidopsis, the root system is mainly composed of the primary root, lateral roots, and root hairs. We review recent studies of the root apical meristem (RAM), discuss the lateral root development, and summarize the research progress about root epidermis—a pivotal interface facilitating root-soil interaction. Furthermore, we shed light on the pivotal role of plant hormones in modulating root development, responding to both internal developmental cues and external environmental signals.