Neurons develop a wide variety of cell-type-specific shapes of dendrites. Nevertheless, the underlying mechanisms remain largely unclear in the mammalian central nervous system in vivo mainly due to the difficulty in observing and manipulating the rapid and non-synchronous changes in dendritic shapes during development. Cerebellar Purkinje cells (PCs), which slowly develop dendrites over several postnatal weeks in a relatively stereotypical manner, have provided an excellent model system. Recent genetic tools have identified two principles that specify the dendritic morphology of PCs. First, the same molecule, such as RORα, T3, and PGC-1α, could exert distinct functions at different developmental stages. Second, competition between dendrites from the same or neighboring PCs likely regulates the extensions of dendrites and their planarity. Furthermore, neuronal activities likely contribute to the maturation and stabilization of dendrites. Future studies are warranted to clarify whether and how defective dendritic growth is related to the pathology of PCs in certain neurological disorders.