Released in July 2018, this report by the NASA Office of Inspector General, Office of Audits, assessed NASA's progress in maximizing utilization of the ISS to accomplish its human exploration objectives and evaluated the options and challenges associated with a transition to commercial operation, potential extension, and the Station's eventual retirement. In meeting these objectives, we interviewed Agency officials, analyzed ISS documentation, reviewed contract and cost data, and visited ISS mission operations at Johnson Space Center.For the past 20 years, the International Space Station (ISS or Station) has served as a platform for humans to learn about living and working in space. NASA's original vision was that the Station would conduct biological and materials research, demonstrate American leadership in space, forge international cooperation, and lead to the commercialization of low Earth orbit. To date, the ISS has accomplished many of these goals by serving as a unique, on-orbit laboratory to study the health effects of space travel on humans and demonstrate new technology - work critical to enable humans to travel deeper into space. However, maintaining and supporting the ISS consumes approximately $3-$4 billion annually, about half of NASA's annual human spaceflight budget.The President's fiscal year (FY) 2019 budget request proposes ending direct Federal funding of the ISS beginning in 2025. If that timetable remains unchanged - an unlikely outcome in light of substantial and bipartisan congressional opposition - NASA would need to manage its remaining time aboard the ISS extremely efficiently in order to complete as much health and human performance and technology-related research as possible. In late March 2018, NASA submitted an ISS Transition Report to Congress that laid out the Agency's plan to transition the Station to commercial operations; however, in light of congressional response to that proposal, the Agency also will need to consider other options, including extending ISS operations until 2028 or beyond. And, at some future point, NASA will need to dispose of the Station via a controlled destructive reentry into the Earth's atmosphere.