The International Space Station (ISS) Environmental Control and Life Support (ECLS) system includes regenerative and non-regenerative technologies which provide the basic life support functions to support the crew, while maintaining a safe and habitable shirtsleeve environment. This paper provides a summary of the U.S ECLS system activities over the past year, covering the period of time between May 1999 and April 2000. Assembly of the ISS has been delayed due to changes in element processing schedules. The 2A.1 logistics flight to ISS occurred in May 1999. The remaining Phase 2 elements have completed most of the element level testing and integration and are approaching final reviews for acceptance for flight. The Phase 3 regenerative ECLS designs have reached the Critical Design Review phase, while several of the Phase 3 elements have held Preliminary or Critical Design Reviews.