In R & D departments of companies, the evaluation of sounds usually is based on physical measurements. However, in "real life", the ultimate judge for sounds is the human hearing system. A customer evaluates the sound of a product by his or her hearing system, not by physical measurement tools, whatever their sophistication may be. In this situation, psychoacoustics is the scientific field of choice to bridge the gap between physical and subjective evaluations. In psychoacoustic experiments, firm relations between the physical representations of sounds and the correlated hearing sensations are established. In practical applications of psychoacoustics, two main tasks can be distinguished: First, questions of sound evaluation, usually for already existing sounds which often have to be improved and Second, questions of sound quality engineering, where for a (new or modified) product or application a suitable sound has to be "tailored". For the evaluation of sounds, basic psychoacoustic magnitudes like loudness and sharpness have proven successful, which assess volume or power and tone color of sounds, respectively. Using these descriptors, extremely different questions like the quality of piano sounds or the annoyance of snoring sounds can be assessed. In addition, psychoacoustic magnitudes related to the temporal structure of sounds like fluctuation strength or roughness can play an important part. In sound quality engineering, for each sound, the right "recipe" has to be found, how to mix the different hearing sensations, to arrive at the desired sound. For the example of warning signals, a systematic approach, incorporating elements of decision tree studies, is discussed.