The electronic structure of ultrathin Cs/Bi2Se3 interfaces has been studied by photoelectron spectroscopy using synchrotron radiation. The experiments were carried out in situ in an ultrahigh vacuum with submonolayer Cs coverages on Bi2Se3 samples. It was found that the adsorption of Cs causes changes in the spectra of the core levels of Bi 4f, Bi 5d, and Se 3d. It has been established that Cs atoms are adsorbed predominantly on Bi atoms in the upper surface layer. The states of the valence band are studied for a clean Bi2Se3 surface and for the Cs/Bi2Se3 interface. Near the Fermi level, 2D topological states have been found. Two induced surface states appear in the region of the valence band upon adsorption of Cs.