The early emission (first few days) of both core-collapse and thermonuclear supernova
explosions is produced as the supernova shock breaks out of the star and interacts with
its surroundings. As such, by observing these bursts of UV, X-ray and sometimes gamma-ray
emission, scientists can probe the progenitors and final stages of evolution of the
progenitors of these cosmic explosions. In this talk, I review the processes producing
this early-time high-energy emission from different supernova types, showing results
from recent calculations. Although astronomers have serendipitously observed this early
SN emission in a few events, a dedicated mission is needed to build a sufficiently
large sample of events to probe the breadth of expected observational features. In
addition, improved models are required to tie these observations to the detail
progenitor properties. I will conclude with a discussion of the future prospects for
the observation and modeling of early emission from supernovae.