  The epochs of origin of the first stars and galaxies, and subsequent growth
of the first supermassive black holes, are among the most fundamental
questions. Observations of the highest redshift Gamma-Ray Bursts (GRBs) will be
the most compelling in situ probe of the history of initial star formation and
consequent epoch of reionization if their prompt and precise detection can be
followed immediately by sensitive near-IR imaging and spectroscopy. Blazars are
the persistent analogs of GRBs and for the same reason (beaming) can be
observed at highest redshifts where they might best trace the high accretion
rate-driven jets and growth of supermassive black holes in galaxies. The
proposed EXIST mission can uniquely probe these questions, and many others,
given its unparalled combination of sensitivity and spatial-spectral-temporal
coverage and resolution. Here we provide a brief summary of the mission design,
key science objectives, mission plan and readiness for EXIST, as proposed to
Astro2010.
