This workshop examined the state-of-the-art of all techniques for measuring radioactivity at ultra-low activity levels as well as all aspects of the development of low-background detectors. Such detectors are needed to study physical processes that can only be observed when all sources of interfering background are reduced to a very low level. These techniques are essential to develop next generation detectors for neutrino research, solar neutrino physics, and neutrino astrophysics, as well as measurement of the double beta-decay process and the search for dark matter in the universe. Topics covered include experimental radio-purity requirements, methods for shielding detectors from cosmic rays and local radioactivity, methods for the measurement of impurities in bulk materials, in gases, and on surfaces, techniques for materials purification, and related subjects. The workshop marked the beginning of excavation for the new international facility for deep underground particle astrophysics (SNOLAB), located in Sudbury, Canada.