A two-day joint US-NZ Workshop on Critical Infrastructure Systems was held in Taupo 10-11th August 2005. This report outlines the background to the Workshop and presents a summary of the discussion highlights. The workshop was a very successful meeting. Twelve high-quality presentations were made on the performance and assessment of critical infrastructure systems. As well, useful exchanges of views and experiences took place during lively break-out and question-and-answer sessions.