  We revisit the microscopic description of AdS$_3$ black holes in light of
recent progress on their higher dimensional analogues. The grand canonical
partition function that follows from the AdS$_3$/CFT$_2$ correspondence
describes BPS and nearBPS black hole thermodynamics. We formulate an entropy
extremization principle that accounts for both the black hole entropy and a
constraint on its charges, in close analogy with asymptotically AdS black holes
in higher dimensions. We are led to interpret supersymmetric black holes as
ensembles of BPS microstates satisfying a charge constraint that is not
respected by individual states. This interpretation provides a microscopic
understanding of the hitherto mysterious charge constraints satisfied by all
BPS black holes in AdS. We also develop thermodynamics and a nAttractor
mechanism of AdS$_3$ black holes in the nearBPS regime.
