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From the beginning, the development of FSI® direct-injection (DI) gasoline engines at Volkswagen was strictly supported by means of optical diagnostics and CFD-simulations. Basic in-cylinder phenomena, such as the formation of the flow field, the penetration of the spray formed by a hollow-cone swirl-type injector at high fuel pressure, the interaction of spray and flow and the formation of an ignitable mixture were analysed in details. The paper describes the laser-optical techniques - particle-image-velocimetry, laser-Doppler-anemometry, video-stroboscopy, high-speed filming and laser-induced fluorescence - which were used during the development of the DI gasoline combustion process. In addition, CFD-simulations have been carried out simultaneously with the experiments, thus providing the engine designer with complete information about the in-cylinder processes to derive further steps of optimization.