The scanning tunneling microscope (STM) enables a large variety of quantum phenomena to be studied with an atomic-scale precision. In particular, inelastic electron tunneling (IET) with the STM is of crucial interest as it allows to locally excite with a high spatial resolution (100 pm) single atoms, molecules, nanocrystals, quantum emitters or plasmonic nanostructures. Excitation can involve vibrational excitation, spin transitions or electronic excitation. There exist mainly two types of IET, resonant IET and radiative IET. In resonant IET, tunneling electrons are resonant with an electronic state (surface state, atomic or molecular state). This resonance results in the exchange of energy between the tunneling electrons and the adsorbate or the surface. In a molecule, very local electronic excitation with a sub-molecular resolution can be exploited to control its dynamics. Radiative IET has a different origine as it is issued from the tunneling current fluctuations. This results in the ability to excite surface plasmons which, in turn, can be used to electronically excite quantum systems.