This book addresses the inherent difficulty in synthesizing single-walled carbon nanotubes (SWCNTs) with well-defined electronic and solubility properties through functionalization, introduction of dopants, topological defects, and intercalation of metals. Depending on the desired application, one can modify the electronic and solubility properties of SWCNTs through an appropriate introduction of imperfections. This scheme broadens the application areas of SWCNTs.