The cubic rare-earth boride series displays diverse electronic states like localized 4 f electron multiplets split by the crystal electric field (CEF), itinerant heavy-fermion quasiparticle bands of the Kondo lattice as well as gapped Kondo insulator or mixed-valent semiconductor states. Furthermore, at low temperatures fairly exotic ordered states may appear due to the "hidden" order of multipoles carried by degenerate CEF multiplets, in addition to common (dipolar) magnetic order present in many RB 6 (R = rare earth) systems. Most prominent are CeB 6 and its La-diluted alloys Rare-Earth Borides Dmytro S. Inosov (ed.