Flux motion and dissipation in high temperature superconductors

An overview of flux motion and dissipation in high T_c superconductors is given. The author outlines aspects on which some consensus exists and then turns to questions which remain more controversial, describing the various experimental and theoretical approaches that have been adopted in probing the behavior of real superconductors. Some recent results on flux motion in SNS (superconductor-normal metal-superconductor) arrays are used to illuminate the duality between descriptions in terms of Josephson junctions and flux motion. It is pointed out that the high anisotropy of the YBCO-class materials and the extremely high anisotropy of the BSSCO class of materials stem from the key role of the strongly superconducting Cu-O planes in their structures