From an examination of the Al(100) surface band structure with high-resolution angle-resolved photoelectron spectra, we identified three surface states. Features in the surface band structure predicted theoretically were confirmed experimentally, including the dispersion of the surface state within the narrow band gap centered at X¯, an avoided crossing between two surface states along Γ¯X¯, and the dispersion of the surface state within the symmetry gap along Γ¯M¯. The electron–phonon coupling strength of the surface state at Γ¯ was determined. Our results indicate that there is no thermally induced defect on Al(100) from 90 to 420K. Our photoemission data serve as reference for future investigation and motivate re-examination of many systems with contemporary photoemission instruments.