||Before it even started the 21st
century has been named the century of live science. Part of this fast
growing field are light sources with their high brilliant light beams
for biology, chemistry and material science. The high scientific
potential of future ERL and FEL light sources has given superconducting
cavity technology an enormous boost in interest. Never before have so
many laboratories and universities worked in the field of s.c.
cavities, and a variety of machines have been proposed for
construction. The envisioned brilliants of the light beams require
excellent electron beam properties beyond present state-of-the-art. The
RF cavity linacs will be the driving engines, and cost efficiency and
emittance preservation will be of great importance. The resulting
challenges for the s.c. cavity technology are manifold and a focus of
the ongoing research work in this field.