A spin filtering device has: a spin filter (1) having an input region (3) for carrying an electron current, an output region (4) for carrying an electron current, and a three-dimensionally confined quantum region (2a) arranged to operate in the Coulomb blockade regime and separating the input and output regions (3 and 4) whereby electrons can only pass from the input region to the output region by tunnelling through the quantum region; and Zeeman splitting means (5) for causing Zeeman splitting in the spin filter, the quantum region (2a) and input and output regions (3 and 4) being formed such that the Zeeman splitting in the input and output regions (3 and 4) is less than the Fermi energy such that, in operation, the spin filter outputs a tunnelling current predominantly of one spin polarity. The direction of Zeeman splitting may be controlled to control the predominant spin polarity.