Particles with sizes of a few nanometers are characterized by imaging, diffraction, and EELS. In-situ experiments are carried out in the TEM to modify the particles and to study their behaviour under different conditions. Electron tomography, in combination with EELS, is used to obtain 3D-information about their structure and composition. The focus is on carbon nanoparticles such as nanotubes, metallic nanocrystals, zeolites, and nanocomposites.