  Hydrogen-rich core collapse supernovae, known as "Type II" supernovae, are
the most common type of stellar explosion realized in nature. They are defined
by the presence of prominent hydrogen lines in their spectra. Type II
supernovae are observed only in star-forming galaxies, and several events have
been directly linked to massive star progenitors. Five main subclasses are
identified: Type IIP (displaying a plateau in their light curve), Type IIL
(displaying a light curve decline), Type IIn (displaying narrow emission
lines), Type IIb (displaying increasingly strong He features with time) and
87A-likes (displaying long-rising light curves similar to that of SN 1987A).
Type IIP supernovae have been robustly established as the explosions of red
supergiants, while the progenitors of Type IIL's remain elusive. Type IIn's are
likely linked to luminous blue variables, Type IIb progenitors may be
interacting binary systems and the prototype of the 87A-like class was observed
to be the explosion of a blue supergiant. The diversity in progenitor mass,
metallicity, binarity and rotation is likely responsible for the diversity in
observed explosion types, but the connection between progenitor parameters and
supernova properties is not yet entirely understood theoretically nor fully
mapped observationally. New observational methods for constraining this
connection are currently being implemented, including the analyses of large
samples of events, making use of very early data (obtained hours to days from
explosion) and statistical studies of host-galaxy properties.
