A classification of magnetic superspace groups compatible with the helical and cycloidal magnetic modulations is presented. Helical modulations are compatible with groups from crystal classes 1, 2, 222, 4, 422, 3, 32, 6 and 622, while cycloidal modulations are compatible with groups from crystal classes 1, 2, m and mm2. For each magnetic crystal class, the directions of the symmetry‐allowed (non‐modulated) net ferromagnetic moment and electric polarization are given. The proposed classification of superspace groups is tested on experimental studies of type‐II multiferroics published in the literature. A classification of the symmetry of magnetic modulations is presented. Helical magnetic ordering is possible only in magnetic superspace groups with proper rotations only, i.e. from classes 1, 2, 222, 4, 422, 3, 32, 6 and 622. Cycloidal modulations are possible in groups from crystal classes 1, 2, m and mm2.