  This paper reexamines the question of vacuum decay in theories of quantum
gravity. In particular it suggests that decay into stable flat or AdS vacua,
never occurs. Instead, vacuum decay occurs, if at all, into a cosmological
spacetime. If the latter has negative cosmological constant, it undergoes a Big
Crunch, which suggests that the whole picture is inconsistent. The question of
decay of de Sitter space must be very carefully defined.
