This chapter discusses the types of cavitation which are very common and whose behaviour can be studied either by theoretical models or by extrapolating the results obtained from experiments on models by using the similitude laws. In particular authors shall see the importance of viscosity, flow velocity and population of nuclei which are the principal parameters. On a geometrically similar configuration at high Reynolds number the boundary layer may be turbulent and hence, there is no separation on the surface of the hydrofoil. It has been observed that the behaviour of the cavity at the trailing region depends on the number of nuclei and hence the number of vapour bubbles present on the profile at a given instant. Therefore, even in the case of a hydrofoil at a small angle of attack, the type of cavitation produced is not always the same; it varies with the experimental conditions.