Fourier transform infrared spectroscopy (FTIR) is a type of spectroscopy known as “vibrational.” Widely used for protein analysis, it also provides a wealth of information on the structure and stability of nucleic acids. Its advantages are that it requires a small amount of sample and that it is easy to vary experimental conditions (pH, temperature, ionic strength, and composition). While numerous reviews describe how to analyze DNA structure alone or in the presence of proteins using FTIR, analyses of RNA are scarce. Nevertheless, RNAs are important factors involved in a multitude of roles in the cell. In this chapter, we present applications of FTIR to analyze RNA structure and how proteins or modified nucleosides may change this structure.