With its extended tunability from the IR to hard X-rays and the exceptional spectral brightness offered by the third generation storage rings, synchrotron radiation (SR) has become an invaluable investigation tool. Major methodological developments have been recently undertaken, first applied to simple systems, isolated atoms and molecules - that can be often modeled ab initio - and then extended to the investigation of more and more complex species, up to the soft and hard condensed matter. Here, we present some of the most recent achievements in SR-based soft X-ray electron spectroscopy applied to the structural characterization of isolated species of increasing complexity from molecules to clusters and nanoparticles. Special attention is devoted to very high-resolution studies of free molecules revealing physical phenomena such as electron diffraction and interference effects, as well as detailed information about the potential energy surfaces. Beyond this, we will see how technical progress of SR-based soft X-ray spectroscopy opens new routes to structural studies on freestanding nanosystems. These achievements have only become possible using the new experimental opportunities offered by the most advanced SR facilities.