In this research notes book, the modelling of mechanical properties of CNT/polymer nanocomposites is presented. The book begins with the structural and intrinsic mechanical properties of CNTs and then introduces computational methods that have been applied to polymer nanocomposites, covering from molecular scale (molecular dynamics, Monte Carlo), microscale (Brownian dynamics, dissipative particle dynamics, lattice Boltzmann, time-dependent Ginzburg–Landau method, dynamic density functional theory method) to mesoscale and macroscale (micromechanics, equivalent-continuum and self-similar approaches, finite element method). Knowledge of the nature and mechanics of the length and orientation of nanotubes, and load transfer between nanotubes and polymers, is critical for the manufacturing of enhanced carbon nanotube polymer composites. It also enables the tailoring of the interface for specific applications or superior mechanical properties. This book discusses the state of these parameters in mechanics of carbon nanotube polymer composites and presents some directions for future research in this field. The book’s aim is to enhance current knowledge in this area to support researchers in carbon nanotubes and help them choose the appropriate modelling tool for accomplishing their research.