Applications of carbon nanotubes in different fields, ranging from nanomedicine to photophysics, have emerged since the discovery of this new carbon structure. Functionalization of the nanotubes enhances solubility, facilitates handling as well as provides a way to introduce new molecular entities that will generate interesting properties. This review focuses on the covalent modification of the surface of nanotubes by means of 1,3-dipolar cycloaddition of azomethine ylides and some recent examples will illustrate the applications of the final products.