Using scanning probe microscopy to study interactions in nanostructures. By combining electrical transport measurements with the spatial information from scanning probe microscopy we can gain new insight into the behavior of electrons inside nanostructures. Currently we are investigating interaction effects inside carbon nanotubes using scanning tunneling microscopy. The 1D nature of nanotubes means that Coulomb interactions are very important, leading to effects such as Luttinger Liquid behavior and the Kondo effect. We are also developing new scanning probe microscopy techniques to image electron wavefunctions inside semiconductor quantum dots. This will allow the study of effects such as electron-electron interactions and coherence in these systems.