Abstract: The concept of “shuttle transport” is introduced into the field of spintronics, and spin-dependent electron transport in magnetic tunnel junctions is studied by considering the coupling of the electronic and mechanical degrees of freedom. It is shown that shuttle transport plays an important role in spin-polarized transport, and can be applied to design spintronic elements. We suggest designs for a spin valve with giant magnetoresistance, a high performance spin injector for semiconductors, and a current diode.