  We refine and extend a recent construction of sets of black hole microstates
with semiclassical interiors that span a Hilbert space of dimension $e^S$,
where $S$ is the black hole entropy. We elaborate on the definition and
properties of microstates in statistical and black hole mechanics. The
gravitational description of microstates employs matter shells in the interior
of the black hole, and we argue that in the limit where the shells are very
heavy, the construction acquires universal validity. To this end, we show it
for very wide classes of black holes: we first extend the construction to
rotating and charged black holes, including extremal and near-extremal
solutions, with or without supersymmetry, and we sketch how the construction of
microstates can be embedded in String Theory. We then describe how the approach
can include general quantum corrections, near or far from extremality. For
supersymmetric black holes, the microstates we construct differ from other
recent constructions in that the interior excitations are not confined within
the near-extremal throat.
