As described in a quote by Nobel laureate Richard E. Smalley, the outstanding electrical and mechanical properties of carbon nanotubes (CNT) offer a very promising future for applications in electronics, as well as being candidates for the targeted improvement of material properties of hybrid CNT systems. Simulation methods from density functional theory to molecular dynamics deliver important results about the intrinsic properties of CNT. But above all they lead to an understanding of the interaction of CNT with external systems in application-relevant situations.