Since the invention of the laser, optical methods have experienced dramatic progress in nearly every field. This holds especially for spectroscopic techniques, such as Raman spectroscopy. If light is scattered on molecules, it is affected by the thermal motion of the molecules. This thermal motion modulates the scattered light in a very characteristic way. We will see that this modulation causes 320the appearance of frequency shifted lines in the scattering spectrum. These frequency shifted spectral lines are called Raman lines. Their frequency shift is a characteristic property of the scattering molecule and its thermodynamic state. Raman scattering is, therefore, used to identify molecules and their thermodynamic state. However, the Raman effect is a very weak effect, and this prevented a wider application until the arrival of the laser, with its unique spectral power density, which made it an ideal light source for Raman scattering. Not only did the classical linear Raman scattering, which got its name from the linear relation between the intensity of the Raman lines and the power density of the incident radiation, get a big boost, but also a number of new nonlinear effects, such as stimulated and coherent Raman scattering, were detected. This chapter will be limited to linear Raman scattering.