We investigate domain-wall/quantum field theory correspondences in various dimensions. Our general analysis does not only cover the well-studied cases in ten and eleven dimensions but also enables us to discuss new cases like a Type I/Heterotic 6-brane in ten dimensions and domain-wall dualities in lower than ten dimensions. The examples we discuss include 'd-branes' in six dimensions preserving 8 supersymmetries and extreme black holes in various dimensions. In the latter case we construct the quantum mechanics Hamiltonian and discuss several limits.