Stringy world branes and exponential hierarchies

We describe heterotic string and M-theory realizations of the RandallSundrum (RS) scenario with N =2 andN = 1 supersymmetry in the bulk. Supersymmetry can be broken only on the world brane, a scenario that has been proposed to account for the smallness of the cosmological constant. An interesting prediction from string duality is the generation of a warp factor for conventional type II Calabi{Yau 3fold compactications. On the other hand we argue that an assumption that is needed in the RS explanation of the hierarchy is hard to satisfy in the string theory context.