Room temperature ionic liquids (RTILs) are very unique substances which may form interfaces with polar and/or non-polar liquids. Though their physico-chemical properties have been investigated intensively, microscopic and local structural knowledge at the interface is limited and the overall problems related to the interface still remain unsolved. In this paper, we have reviewed our series of experimental results on surfaces or buried interfaces (liquid/liquid interfaces) by using IR-Vis sum-frequency generation vibrational spectroscopy. We demonstrate for the first time the formation of a nonpolar alkyl-chain dividing layer between RTIL ([C₄mim]PF₆) and an n-alcohol. Heterogeneous and complex systems of such interfaces may explain various functions of ionic liquids occurring at the interfaces.