GaN nanocolumns, which are one-dimensional nanocrystals with diameters of less than several hundred nanometers, have been self-organized by radio-frequency-plasma-assisted molecular beam epitaxy (RF-MBE) and subsequently extensively studied. In this chapter, studies on GaN-based nanocolumns performed at Sophia University are systematically reviewed. These studies have addressed the first self-organization of nanocolumns, visible-light-emitting InGaN-based nanocolumns, the nanocrystal effects of such nanocolumns, controlled growth of regularly arranged nanocolumns by MBE, and application of GaN nanocolumns to nanocolumn light emitters. Achievements in research on GaN-based nanocolumns by other groups are described in the subsequent chapters.