Fifty years after the founding of NASA, from 28 to 29 October 2008, the NASA History Division convened a conference whose purpose was a scholarly analysis of NASA's first 50 years. Over two days at NASA Headquarters, historians and policy analysts discussed NASA's role in aeronautics, human spaceflight, exploration, space science, life science, and Earth science, as well as crosscutting themes ranging from space access to international relations in space and NASA's interaction with the public. The speakers were asked to keep in mind the following questions: What are the lessons learned from the first 50 years? What is NASA's role in American culture and in the history of exploration and discovery? What if there had never been a NASA? Based on the past, does NASA have a future? The results of those papers, elaborated and fully referenced, are found in this 50th anniversary volume. The reader will find here, instantiated in the complex institution that is NASA, echoes of perennial themes elaborated in an earlier volume, Critical Issues in the History of Spaceflight. The conference culminated a year of celebrations, beginning with an October 2007 conference celebrating the 50th anniversary of the Space Age and including a lecture series, future forums, publications, a large presence at the Smithsonian Folklife Festival, and numerous activities at NASA's 10 Centers and venues around the country. It took place as the Apollo 40th anniversaries began, ironically still the most famous of NASA's achievements, even in the era of the Space Shuttle, International Space Station (ISS), and spacecraft like the Mars Exploration Rovers (MERs) and the Hubble Space Telescope. And it took place as NASA found itself at a major crossroads, for the first time in three decades transitioning, under Administrator Michael Griffin, from the Space Shuttle to a new Ares launch vehicle and Orion crew vehicle capable of returning humans to the Moon and proceeding to Mars in a program known as Constellation. The Space Shuttle, NASA's launch system since 1981, was scheduled to wind down in 2010, freeing up funds for the new Ares launch vehicle. But the latter, even if it moved forward at all deliberate speed, would not be ready until 2015, leaving the unsettling possibility that for at least five years the United States would be forced to use the Russian Soyuz launch vehicle and spacecraft as the sole access to the ISS in which the United States was the major partner. The presidential elections a week after the conference presaged an imminent presidential transition, from the Republican administration of George W. Bush to (as it turned out) the Democratic presidency of Barack Obama, with all the uncertainties that such transitions imply for government programs. The uncertainties for NASA were even greater, as Michael Griffin departed with the outgoing administration and as the world found itself in an unprecedented global economic downturn, with the benefits of national space programs questioned more than ever before. There was no doubt that 50 years of the Space Age had altered humanity in numerous ways ranging from applications satellites to philosophical world views. Throughout its 50 years, NASA has been fortunate to have a strong sense of history and a robust, independent, and objective history program to document its achievements and analyze its activities. Among its flagship publications are Exploring the Unknown: Selected Documents in the History of the U.S. Civil Space Program, of which seven of eight projected volumes were completed at the time of the 50th anniversary. The reader can do no better than to turn to these volumes for an introduction to NASA history as seen through its primary documents. The list of NASA publications at the end of this volume is also a testimony to the tremendous amount of historical research that the NASA History Division has sponsored over the last 50 years, of which this is the latest volume.