  In these lecture notes we review the various relations between intersection
theory on the moduli space of Riemann surfaces, integrable hierarchies of KdV
type, matrix models, and topological quantum field theories. We explain in
particular why matrix integrals of the type considered by Kontsevich naturally
appear as tau-functions associated to minimal models. Our starting point is the
extremely simple form of the string equation for the topological (p,1) models,
where the so-called Baker-Akhiezer function is given by a (generalized) Airy
function.
