Since the 1986 discovery of high‐temperature superconductors, researchers have been struggling to understand the nature of the magnetic flux lines that thread through these copper‐oxide materials when the field is above a few tens of gauss. the flux lines take the form of vortices, swirling supercurrents that confine the magnetic field to a cylindrical region around a quiescent center. Understanding them is more than an academic exercise: Motion of the vortices, when pushed by a high enough current, introduces resistivity and limits the long‐sought high‐field applications. (SeePHYSICS TODAY, October 1992, page 17.