Carbon nanotubes are certainly the most studied nanomaterials ever, considering the cumulated number of papers devoted to them since the 1990s (Fig. 1.1). Only graphene will possibly overcome nanotubes in this regard one day, specifically because of the boosting effect of the Nobel Prize dedicated to it in 2010. But it cannot be ignored that carbon nanotubes are primarily based on graphene, and understanding carbon nanotube properties (and any other graphene-based materials indeed) requires describing graphene properties first.