This paper briefly presents the history, interactions and current activities of NASA's Near-Earth Object Program Office. The Program Office utilizes near-Earth object (NEO) astrometric data from the international community, received from the Minor Planet Center, to refine orbits and provide predictions for coming Earth close approaches. For those objects for which an Earth impact cannot be ruled out, an automatic Sentry system computes Earth impact probabilities. These predictions are often compared and verified with a similar process that is underway in Pisa Italy (NEODyS). The sophisticated techniques used within the Sentry system are described. Recent studies of some of the issues surrounding the deflection of an Earth threatening NEO are also described. In particular, the viability of the gravity tractor concept is discussed in connection with avoiding an asteroid's passage through a dynamical keyhole at the time of a close Earth approach - an event that ensures a subsequent Earth impact event at a later time.