Research on para- and orthohydrogen is reviewed, from the assumption of two different nuclear spin species of the hydrogen molecule by Hund, and their catalytic transformation by Bonhoeffer and Harteck, to modern applications of the solid parahydrogen crystal. During the ascent of quantum mechanics the hydrogen atom and molecule served as critical test systems for many theoretical concepts. In recent years spectroscopy of the condensed phases of molecular hydrogen has helped to understand the transition from microscopic interactions to macroscopic bulk properties. This special role is due to the small magnitude of intermolecular interactions between hydrogen molecules and the unique quantum properties of hydrogen in the solid phase. Two very new fields, namely the use of solid parahydrogen as matrix medium and as a crystal for nonlinear optics, are discussed.