  Measurements of the decay strength of superallowed 0+ to 0+ nuclear beta
transitions shed light on the fundamental properties of weak interactions.
Because of their impact, such measurements were first reported 60 years ago in
the early 1950s and have continued unabated ever since, always taking advantage
of improvements in experimental techniques to achieve ever higher precision.
The results helped first to shape the Electroweak Standard Model but more
recently have evolved into sensitively testing that model's predictions. Today
they provide the most demanding test of vector-current conservation and of the
unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Here, we review the
experimental and theoretical methods that have been, and are being, used to
characterize superallowed 0+ to 0+ beta transitions and to extract
fundamentally important parameters from their analysis.
