Large-area single-layer WS2 is grown epitaxially on Au(111) using evaporation of W atoms in a low pressure H2S atmosphere. It is characterized by means of scanning tunneling microscopy, low-energy electron diffraction, and core level spectroscopy. Its electronic band structure is determined by angle-resolved photoemission spectroscopy. The valence-band maximum at (K) over bar is found to be significantly higher than at (Gamma) over bar. The observed dispersion around (K) over bar is in good agreement with density functional theory calculations for a free-standing monolayer, whereas the bands at (Gamma) over bar are found to be hybridized with states originating from the Au substrate. Strong spin-orbit coupling leads to a large spin-splitting of the bands in the neighborhood of the (K) over bar points, with a maximum splitting of 419(11) meV. The valence-band dispersion around (K) over bar is found to be highly anisotropic with spin-branch dependent effective hole masses of 0.40(02)m(e) and 0.57(09)m(e) for the upper and lower split valence band, respectively. The large size of the spin splitting and the low effective mass of the valence-band maximum make single-layer WS2 a promising alternative to the widely studied MoS2 for applications in electronics, spintronics, and valleytronics.