A wide aperture permanent magnet structure which is useful in creating a highly uniform longitudinal or solenoidal magnetic field in the working region of the magnet and in which the aperture of the structure can be equal in cross-sectional area to the working region of the magnet. The geometry and magnetization direction of the constituent magnets are chosen to maximize the uniformity of the longitudinal or solenoidal magnetic field in the working region of the magnet while minimizing the overall volume and weight of the structure as well as eliminating the need for magnetic pole pieces made of iron or other high permeability materials. The invention can take the form of a cylindrical shell of permanent magnets to create a solenoidal magnetic field, or a parallel surface arrangement to create a longitudinal magnetic field.