This paper is an introduction to the language of Feynman Diagrams. We use
Reshetikhin-Turaev graphical calculus to define Feynman diagrams and prove that
asymptotic expansions of Gaussian integrals can be written as a sum over a
suitable family of graphs. We discuss how different kind of interactions give
rise to different families of graphs. In particular, we show how symmetric and
cyclic interactions lead to ``ordinary'' and ``ribbon'' graphs respectively. As
an example, the 't Hooft-Kontsevich model for 2D quantum gravity is treated in
some detail.Comment: 30 pages, AMS-LaTeX, 19 EPS figures + several in-text XY-Pic,
PostScript \specials, corrected attributions, 'PROP's instead of 'operads
