Novel ground states might be realized in honeycomb lattices with strong spin-orbit coupling. Here we study the electronic structure of α−RuCl3, in which the Ru ions are in a d5 configuration and form a honeycomb lattice, by angle-resolved photoemission, x-ray photoemission, and electron energy loss spectroscopy supported by density functional theory and multiplet calculations. We find that α−RuCl3 is a Mott insulator with significant spin-orbit coupling, whose low energy electronic structure is naturally mapped onto Jeff states. This makes α−RuCl3 a promising candidate for the realization of Kitaev physics. Relevant electronic parameters such as the Hubbard energy U, the crystal field splitting 10 Dq, and the charge transfer energy Δ are evaluated.