Book excerpt: This book compiles all current information on the different types of functionalization of carbon nanotubes (CNTs) and graphene, both covalent and non-covalent. The book starts with a general overview of the synthesis, characterization and application of functionalized CNTs and graphene. Special attention is dedicated to the characterization of functionalized materials, a topic rarely addressed on the literature. The authors provide a comparison between the functionalization of these two types of carbon materials.