Fullerenes, hollow carbon cages on the order of 1 nm in diameter, are future building blocks in many areas of applied and fundamental nanoscience. Fullerenes show potential for applications in nanotechnology due to the possibility of tuning their properties by doping and/or functionlization. In particular, the endohedral doping of the hollow carbon cage with metal atoms and clusters allows changing of the electronic and magnetic properties of the molecule without significant distortion of the geometry of the outer shell. Despite their outstanding applications in technology and in bio-medical sciences the limited availability of endohedral metallofullerenes has hindered studies that describe their electronic and structural properties, the knowledge of which are essential prerequisites for many nanotechnological applications. In this book, we present our results on the characterization (structural, electronic and vibrational) of cerium endohedral fullerenes and provide precious clues about the formation mechanism of these species at the nanoscale.