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Progress in the development of calculating machines has led to modern computers that represent and treat data digitally. In principle, the physical platform on which computation is done is irrelevant: A digital computer can be realized with vacuum tubes, discrete transistors, integrated circuits, pneumatic valves, or optical logic gates. However, digital optical computing is not the only way in which computing can be done with light. On page 160 of this issue, Silva et al. (1) show theoretically that the direct manipulation of light waves can offer extraordinary possibilities toward analog computing. Instead of representing quantities by discrete bits, the input and output data are expressed as continuous electric fields of light. The necessary mathematical operations are realized through the interaction of the wave with metamaterials, microstructured composites that respond in ways that cannot be realized in isotropic materials (2). Furthermore, the wavelength-scale dimensions of such computing machines make them extremely compact.