Controlling reversible dielectric breakdown in metal/poly mer nanocomposites is reported on page 1850 by J. Kim and B. A. Grzybowski. The image illustrates reversible dielectric breakdown of an array of metal nanorods embedded in a polymer matrix and subject to an electric bias. The breakdown occurs in a threshold-like fashion such that the nanocomposite material can be repeatedly “cycled” between low- and high-conductance states. The breakdown voltage can be adjusted by engineering the properties of the polymer matrix.