  A unified evolutionary scheme that includes post-AGB systems, barium stars,
symbiotics, and related systems, explaining their similarites as well as
differences. Can we construct it? We compare these various classes of objects
in order to construct a consistent picture. Special attention is given to the
comparison of the barium pollution and symbiotic phenomena. Finally, we outline
a `transient torus' evolutionary scenario that makes use of the various
observational and theoretical hints and aims at explaining the observed
characteristics of the relevant systems.
