  The Asymptotic Giant Branch (AGB) phase is very short but its importance is
seen in its nucleosynthesis. A revolution in stellar modelling has taken place
in the last 20 years, inspired jointly by this rich nucleosynthesis and partly
by new data. For example, the isotopic data coming from pre-solar grains (see
this volume) forces theorists to include species that were previously ignored,
species which are energetically of no importance (i.e. they play no role in
determining the stellar structure) but which can be used to constrain the
models. Nucleosynthesis is now important as a tracer of temperature and mixing,
and not simply a by-product of energy generation. But along with these advances
come more quantitative demands. It is now increasingly important to know what
is known well and what is less sure. This is the goal of this paper.
