The problem of predicting the behavior of the incompressible turbulent boundary layer in an adverse pressure gradient is re-examined. An outline of the problem is given along with a brief summary of the work that has already been done, including both experimental investigation are presented for a separating turbulent boundary layer with various pressure distributions. An approximate theory is developed in which the momentum integral equation is satisfied for each half of the boundary layer. The velocity profiles used in the analysis consist of the well known wall and wake regions, resulting in a two-parameter family with the Reynolds number as one parameter. It is assumed, with some experimental justification, that the eddy viscosity can be reasonably approximated from zero pressure gradient experimets. The numerical calculations, using the Runge-Kutta procedure, show good agreement with the experiments. The reliability that can be expected of such approximate methods is discussed. (Author).