  We propose a theory of degenerations for derived module categories, analogous
to degenerations in module varieties for module categories. In particular we
define two types of degenerations, one algebraic and the other geometric. We
show that these are equivalent, analogously to the Riemann-Zwara theorem for
module varieties. Applications to tilting complexes are given, in particular
that any two-term tilting complex is determined by its graded module structure.
