In 1852, W. Weber invoked Faraday’s law to suggest that natural diamagnetism could be produced by currents induced in microscopic conducting closed loops, which would be present inside matter. Spirals are well-known designs, widely used in planar microwave circuits as small-size inductors and resonators. However, spirals are low-symmetry structures and, in particular, they do not show inversion symmetry. Therefore, in spite of the fact that a quasi-static analysis does not predict them, bianisotropy and other cross-polarization effects can be present in metamaterials made from spiral resonators. Split ring resonators (SRRs) provide a simple and effective way for designing magnetic metamaterials with negative parameters. The behavior of SRRs at infrared and optical frequencies can be obtained from a straightforward extension of the aforementioned LC circuit model. The main effects at these frequencies are the saturation in the SRR frequency of resonance and a strong decrease in the SRR magnetic response.