The sub-nanometer cavity of fullerenes is an ideal platform to host a variety of metallic clusters, forming endohedral metallofullerenes (EMFs). They display unique structures and fascinating properties, with a variety of potential applications, with prospective devices based on EMFs being expected in the near future. This Reprint provides information on state of the art in the research of EMFs, mainly focusing on the theoretical results of the formation mechanism (even for analogous metalloborospherene), bonding properties, and stability of single molecules and even oligomers/polymers, in addition to experimental achievements on new species with non-IPR cages and unconventional actinide metal cores, novel chemical reactivity, and even the vibrational properties of solid materials, from a wide range of active researchers around the world. It is our hope that this Reprint acts as a guide to a broad readership who are interested in entering this field.