Constrained approximation in Sobolev spaces Positive, copositive, onesided and intertwining (co-onesided) polynomial and spline approximations of functions $f\in\Wp^k\mll$ are considered. Both uniform and pointwise estimates, which are exact in some sense, are obtained. Keywords:Constrained approximation, polynomials, splines, degree of, approximation, $L_p$ space, Sobolev spaceCategories:41A10, 41A15, 41A25, 41A29