This paper describes an innovative haptic interface device based on magneto-rheological fluid (MRF). A system of permanent magnets and coils is designed in order to produce a proper distribution of a magnetic field inside the fluid. This distribution, with its spatial resolution, causes the MRF to assume prescribed shapes and softness profiles that can be directly felt and explored by hand. The device is designed using a 3-D finite-elements code taking into account the B-H functions of the nonlinear materials (MRF, permanent magnets, ferromagnetic materials). In order to validate the finite-element model, some experimental magnetic measurements are taken on a simplified prototype. Furthermore, the maps of the flux density and those of the shear stress inside the fluid are carefully analyzed. Finally, the interaction between the operator's hand and the MRF is numerically investigated.