Liquid crystals are characterized by an orientational order of the rod‐like (or possible disk‐like) molecules of which they are composed. The anisotropic part of the molecular diamagnetic susceptibility gives rise to a coupling between external magnetic fields and the orientational structure. In terms of the Frank elasticity theory we discuss several such effects of a static field, e.g. unwinding of a cholesteric helix, Freedericksz transition. The second part of this review is devoted to a consideration of magnetic resonance as a tool to study both the order parameter and the orientational fluctuation modes in a liquid crystal.