This chapter summarizes the state of the art in the field of Janus and patchy particles, with a broad introduction on the main general synthetic procedures and then narrowing down to the case of metallic heterostructures. All the synthetic procedures were additionally classified into three main approaches to simplify the wide variety of available techniques: phase separation, self-assembly; and masking processes. The chapter presents an over view of the main properties and applications of metallic Janus particles, derived in most cases from their metallic components, such as: optical response, catalysis, self-assembly, drug delivery, etc. It discusses selected general synthetic procedures for the preparation of Janus and patchy particles. Phase separation methods have been strongly developed to prepare metallic heterodimers comprising metal oxides or polymers. The main advantages of these procedures rely on their ability to produce Janus particles in one step and also in large amounts.