Boron nitride (BN) nanostructures can have varied structures. ey can simply be nanoscale particles of various bulk BN materials, including hexagonal-phase BN (h-BN) and cubic-phase BN (c-BN). However, many of the BN nanostructures of popular interest were discovered in the past 20 years and are unique in their structures and properties. ese include BN nanotubes (BNNTs), BN nanosheets (BNNSs), and BN nanoribbons (BNNRs). Furthermore, some new functional BN nanostructures were recently demonstrated by the authors including quantum dots functionalized BNNTs (QDs-BNNTs) and branching CNT-BNNT heterojunctions. e controlled growth and interesting properties of these nanostructures will be described in this chapter. Prior to the detailed discussions in subsequent subsections, a brief introduction of bulk BN phases is described here as a reference and comparison for the later discussed BN nanostructures.