  In this paper we consider minors of ribbon graphs (or, equivalently,
cellularly embedded graphs). The theory of minors of ribbon graphs differs from
that of graphs in that contracting loops is necessary and doing this can create
additional vertices and components. Thus the ribbon graph minor relation is
incompatible with the graph minor relation. We discuss excluded minor
characterisations of minor closed families of ribbon graphs. Our main result is
an excluded minor characterisation of the family of ribbon graphs that
represent knot and link diagrams.
