[en] The linear and nonlinear evolution of the plane magnetized jet, a magnetohydrodynamic configuration consisting of a plane fluid jet embedded in a neutral sheet, is examined. At low Alfvacute en number (A=ratio of the characteristic Alfvacute en speed to the characteristic flow speed), two ideally unstable modes are found that correspond to the sinuous and varicose modes of the fluid plane jet. Increasing A leads to a stabilization of both of these modes. For large A there is a separate resistively unstable mode. The ideal varicose mode and the resistive varicose mode are distinct modes with similar properties in a given range of A. A magnetohydrodynamic generalization of the Howard semicircle theorem indicates that a strong enough magnetic field will damp out all ideal modes. The stability properties of the two modes are studied in terms of their perturbation energy balances. The nonlinear evolution is quite different for the three modes in terms of time scales and of the properties and spatial location of the small-scale structures that strongly modify the initial configuration. The two ideal modes have in common the capability of accelerating the fluid initially at rest in a much more efficient way than the resistive one. copyright 1998 American Institute of Physics