Hole transporting properties and energy barriers at organic-organic interfaces relevant to electrophotographic and organic electroluminescent (EL) devices are described. Three wellknown hole transporting molecules, 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC), N,N′- diphenyl-N,N′-bis(1 -naphthyl)-(1,1 ′-biphenyl)-4,4′-diamine (NPB), and N,N,N′,N′-tetrakis(4- tolyl)-(1,1 ′-biphenyl)-4,4′-diamine (TTB) are used in this study. The ionization potentials (IP) and oxidation potentials (Eox) of these materials are determined by photoemission spectroscopy and electrochemical measurements, from which a conversion formula is obtained (IP ∼ 4.5 eV + eEox). Hole transport across organic-organic interfaces is investigated by time-of-flight transient photocurrent techniques. The efficiencies of hole injection are consistent with the energy barriers, when present, at these interfaces.