Probe beam deflection (PBD) techniques are a set of in situ electrochemical methods based on the measurement of refractive index gradients in front of the electrode/electrolyte interface. Here, the details of the techniques are described. First, the theory of potential step chronodeflectometry and pulse voltadeflectometry is discussed. Later, different numerical procedures used for data processing and/or simulation of cyclic voltadeflectometry experiments are described. Then, an overview is performed of the techniques use to study electrochemical systems. The systems described are limited to surface species in binary electrolytes, where a clear interpretation of the data is possible. Among the systems studied are: surface reactions on solid electrodes, electrochromic oxides, conducting polymers, redox polymers, double layer charging in nanostructured carbons and ion exchange in layer-by-layer self assembled multilayers. It is shown that PBD techniques have been able to ascertain the effect of different factors on ion exchange: anion size, pH, solvent, film composition, covalent modification, etc. The capability of the techniques to perform fast measurements was also used with success to find out kinetic effects on the ion exchange.