The technique developed in the general theory of discontinuities is applied to the basic equations of unsteady magnetohydrodynamics in order to find the conditions to be satisfied by the discontinuities in the derivatives of the significant flow and magnetic field parameters. In the formulation of the basic equations use is made of the ``magnetohydrodynamic approximation.'' This amounts to the assumption that the magnetic energy is very large compared with the electric energy, or physically, that the displacement current is negligible. The fluid itself is considered to be infinitely conductive, inviscid, and compressible. With the aid of the relations satisfied by the jumps in the derivatives of the parameters the various characteristic manifolds are found. Finally, it is shown that these manifolds are hypersurfaces along which small disturbances and weak shocks are propagated.