Book excerpt: Applications of superconductivity at the boiling temperature of liquid nitrogen continue to challenge physicists, materials scientists and engineers all over the world eight years after the discovery of high temperature superconductivity. The key to a solution of today's problems lies in the optimization of the defect structure in well-oriented oxide materials as well as in a fundamental understanding of the magnetic microstructures in the mixed state and how they are affected by the crystallographic nature ('dimensionality') of these materials. Fifteen invited overview lectures as well as approximately 150 contributed papers highlight the state of the art in this important field of superconductivity and review our current knowledge of critical currents in superconductors.