Recent studies on the Rashba effect on surfaces are reviewed. The Rashba effect refers to the k-dependent spin splitting of valence bands due to spin-orbit coupling in two-dimensional systems under out-of-plane electric field. After the physical mechanism of the Rashba effect is briefed, experimental and theoretical studies since the surface Rashba effect was first demonstrated for Au(111) in 1996 are surveyed with an emphasis placed on the microscopic origin of the giant Rashba spin splitting on surfaces covered with monolayer films of heavier elements. Most recently, giant Rashba spin splitting was realized on the surface of semiconductors, which serves a possibility of spintronic application of the surface Rashba effect.