We study the stability of the neutral and charged pion-condensed phases of nuclear matter against fluctuations of the order parameter. At finite temperatures pion condensates with an order parameter varying in only one dimension are, as we show, prohibited, while such condensates are allowed at zero temperature. Condensates that vary in two and three dimensions can be stable at all temperatures. Another allowed state, which may be favored energetically, is a quasi-ordered one-dimensional condensate characterized by long-range pion field correlations decaying only algebraically in space; insufficient experimental resolution may, however, limit one's ability to distinguish such a one-dimensional structure from true one-dimensional long-range order. Finally, we calculate the normal modes and the pion propagator in a charged one-dimensional running-wave condensate, explicitly illustrating the effect of long-range Coulomb forces on the order-parameter fluctuations. © 1982.