  In these notes we explore a variety of models comprising a large number of
constituents. An emphasis is placed on integrals over large Hermitian matrices,
as well as quantum mechanical models whose degrees of freedom are organised in
a matrix-like fashion. We discuss the relation of matrix models to
two-dimensional quantum gravity coupled to conformal matter. We provide a brief
overview of a variety of more general quantum mechanical matrix models and
their putative worldsheet interpretation, as well as other recent developments
on large $N$ systems. We end with a discussion of open questions and future
directions.
