Seeing the Nature of the Accelerating Physics: It's a SNAP

For true insight into the nature of dark energy, measurements of the precision and accuracy of the Supernova/Acceleration Probe (SNAP) are required. Precursor or scaled-down experiments are unavoidably limited, even for distinguishing the cosmological constant. This white paper presents an overview of the necessity for SNAP and the role of precursor experiments; accompanying white papers detail the supernovae and weak lensing parts of the experiment.