The dimensionality of electronic states determines a number of physical phenomena such as phase transitions, transport, or superconductivity. Employing scanning tunneling microscopy combined with angle-resolved photoemission spectroscopy we demonstrate how the dimensionality of electronic states can be continuously tuned from three to two dimensions. This is achieved by adsorption of nanowires on surfaces of layered crystals without changing the chemical composition of the material. Exemplary results for Rb nanowires on TiTe2 are discussed with the help of electronic structure calculations.