A stable set of beliefs is defined to be a subset of the set of sequen
tial equilibria such that for any equilibrium in the subset the belief
s and/or actions at any information set should be consistent with the
equilibria in the subset that reach that information set. Further, any
sequential equilibrium that is not in the subset disagrees, at some u
nreached information set, with the equilibria of the subset that do re
ach that information set. The behavior of this solution is examined in
a number of examples and is contrasted with the behavior of other sol
ution concepts.