  Compared with ordinary spirals, the ISM in ring galaxies experiences markedly
different physical conditions and evolution. As a result, ring galaxies provide
interesting perspectives on the triggering/quenching of large scale star
formation and the destructive effects of massive stars on molecular cloud
complexes. We use high resolution radio, sub-millimeter, infrared, and optical
data to investigate the role of gravitational stability in star formation
regulation, factors influencing the ISM's molecular fraction, and evidence of
peculiar star formation laws and efficiencies in two highly evolved ring
galaxies: Cartwheel and the Lindsay-Shapley ring.
