In the next decade Type Ia supernovae (SNe Ia) will be used to test theories
predicting changes in the Dark Energy equation of state with time. Ultimately
this requires a dedicated space mission like JDEM. SNe Ia are mature
cosmological probes --- their limitations are well characterized, and a path to
improvement is clear. Dominant systematic errors include photometric
calibration, selection effects, reddening, and population-dependent
differences. Building on past lessons, well-controlled new surveys are poised
to make strides in these areas: the Palomar Transient Factory, Skymapper, La
