The water surface is more challenging than the bulk computationally as well as experimentally, because the force fields of water for MD simulations are tuned mostly as regards the bulk properties. This makes surface-selective vibrational spectroscopy even more important not only for investigating the structure and dynamics of the water surface but also for examining and developing excellent water models at the surface. This chapter describes the application of the quantum/classical mixed approach to sum frequency generation spectroscopy of the air/water interface.