An analytic relation for determining the length of the shock-laminar or turbulent boundary layer interaction zone is obtained on the basis of an analysis of the boundary layer separation criterion. It is shown that as the Mach number of the flow increases, the interaction length decreases, and that with increase in the Reynolds number it behaves nonmonotonically: in the laminar region it increases, while on transition to the turbulent regime it falls sharply and then varies along a curve with a maximum. The results of the calculations are in satisfactory agreement with the existing experimental data.