A great variety of methods for the evaluation of cavitation erosion are now available. However, because of a lack of correlation with the hydromechanics of cavitation, they fail to provide a solution to the problem of scale effects. Studies are described of the hydromechanical aspects of cavitation erosion induced in the wake of a circular profile model for plane flow conditions in a water tunnel. An energy parameter for the estimation of resistance of materials to cavitation damage will be introduced. An explanation of cavitation effects will be reached by varying the parameters likely to affect the intensity and development of erosion. These parameters include: the state and structure of the cavitation zone, relative dimensions of the model, cavitation layer thickness, the characteristic model dimension, flow velocity, specimen erosion volume, experimental duration, and Reynolds and Weber numbers. The energy parameter is derived in terms of the erosion volume and the work done by the cavitation drag forces. The reciprocal value of the energy parameter gives the erosion resistance of the material in terms of the amount of work done in damaging unit volume of the material. This parameter is used to explain the power law obeyed by dimensional and velocity scale numbers. It will be shown that erosion volume is proportional to flow velocity to the fifth power, and to the characteristic model dimension to the third power. The conditions for prognosis of erosion volume from the experiments with models will be specified.