The adsorption of catechol (1,2-benzendiol) on the anatase TiO2(101) surface was studied with synchrotron-based ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). Catechol adsorbs with a unity sticking coefficient and the phenyl ring intact. STM reveals preferred nucleation at step edges and subsurface point defects, followed by ID growth and the formation of a 2 x 1 superstructure at full coverage. A gap state of similar to 1 eV above the valence band maximum is observed for dosages in excess of similar to 0.4 Langmuir, but such a state is absent for lower coverages. The formation of the band gap states thus correlates with the adsorption at regular lattice sites and the onset of self-assembled superstructures.