In this proceeding I will review the current advancements in the context of rare semileptonic decays of hadrons. Such processes suffer different sources of suppression within the Standard Model and are, in fact, the most appealing places to look for possible effects of New Physics. I will discuss the state-of-the-art of phenomenological studies of semileptonic neutral-current $B_{(s)}$-meson decays with charged leptons in the final state. In particular, I will focus on various approaches to the description of the hadronic form factors, which encode all the information about strong interactions among the quarks. I will then move to the state-of-the-art of theoretical studies and experimental analyses of rare semileptonic decays with di-neutrinos in the final state. Some interesting developments for the future will be finally discussed.