Low-dimensional and nanoparticulate materials such as thin films, nanoparticles and clusters often exhibit unique properties that are very different from those of their atomic and bulk counterparts. This opens new possibilities for fabrication of highly functional materials with tailored properties. However, the prerequisite for the development of such materials is their detailed characterization at an atomic level. Due to the limitations of both theory and experiments this task can very often only be achieved combining computer simulations and experimental investigations. The examples presented in my talk include joined theoretical and experimental studies of new building blocks for cluster-assembled materials, structure evolution of nanoparticulate iron oxide starting from small clusters through to nanoparticles as well as investigations of various phenomena on silica surfaces. In all cases the full characterization of these systems could only be accomplished combining experiments and computational investigations.