The well-known result for the stability of a plane vortex sheet in an incom-pressible fluid is generalized to include magnetic fields and three-dimensional effects. The resulting current-vortex sheet is shown to be stabilized by sufficiently strong magnetic fields, and weaker fields are shown to give a partial stability. The effect of walls is examined, and in general, they are found to add to the stability of the flow. The dispersion relationships are found for several configurations of walls and current-vortex sheets, and conditions for stability are given.