Observations of SNe light at early times can open a window to a wealth of information
on the progenitor system and the explosion itself. I will present the theoretical
expectation of that emission, starting at the shock breakout, through the planar
phase and into at the spherical phase, until recombination and/or radioactive decay
start playing a role. I will discuss separately Newtonian breakout and relativistic
breakout. The former take place in regular core-collapse SNe while the latter is
expected in white dwarf explosions (e.g., type Ia and .Ia SNe, AIC), extremely
energetic SNe (e.g., SN2005ap, SN2007bi) and GRB-SN. I will show that both types of
breakouts, when spherical, have characteristic signatures, which can be identified,
and discuss the detectability of the breakout emission from various types of SNe.