  We motivate the cosmological science case of measuring Type Ia supernovae
with the Nancy Grace Roman Space Telescope as part of the High Latitude Time
Domain Survey. We discuss previously stated requirements for the science, and a
baseline survey strategy. We discuss the various areas that must still be
optimized and point to the other white papers that consider these topics in
detail. Overall, the baseline case should enable an exquisite measurement of
dark energy using SNe Ia from z=0.1 to z>2, and further optimization should
only strengthen this once-in-a-generation experiment.
