Electron energy loss spectroscopy (EELS) has become a very important tool in the study of the surface chemistry of solids. Besides providing information on the vibrational spectra of adsorbed molecules, EELS (with primary electrons of low energy, ≤5 eV) also throws light on metal-ligand vibrations. The vibrational spectra from EELS are useful in understanding gas-solid interactions and the nature of the molecular species such as the state of hybridization of orbitals in hydrocarbon fragments bound to the surface. By employing primary electrons of higher energies (30–300 eV), electronic excitations of adsorbed molecules as well as the adsorbents themselves can be fruitfully studied. This article describes the up-to-date status of EELS in the study of adsorbed molecules and surveys all the important literature data and correlations.