The inducibility of graphs

We investigate the maximum number of ways in which a k-vertex graph G can appear as an induced subgraph of an n-vertex graph, for n ≥ k. When this number is expressed as a fraction of all k-vertex induced subgraphs, it tends to a definite limit as n → ∞. This limit, which we call the inducibility of G, is an effectively computable invariant of G. We examine the elementary properties of this invariant: its relationship to various operations on graphs, its maximum and minimum values, and its value for some particular graphs.