Spin-polarized two-electron spectroscopy-in-reflection has been proven to be a very efficient technique for studying the exchange correlation and spin-orbit interaction on magnetic and non-magnetic surfaces and thin ferromagnetic films. The essence of the technique is the detection of two time-correlated electrons emitted from the sample surface upon an impact of a single incident electron and measurements of their momenta. The coincidence technique has been combined with a time-of-flight electron energy analysis to measure momentum distributions of correlated electron pairs for various orientations of the electron beam polarization relative to the scattering plane and magnetization of the sample. This set of measurements allows to extract the information on exchange correlation and spin-orbit interaction from measured spectra. Energy- and momentum-conservation in the electron-electron scattering allows the valence electron involved into collision to be located in the energy-momentum space of the valence band of the sample. In this way the energy and momentum location of the exchange and SOI can be established. A few examples of the application of this technique for studying ferromagnetic and non-magnetic surfaces are presented.