Quantum ergodicity'' usually deals with delocalization properties of eigenfunctions of the Laplacian on compact manifolds. After a review of the subject, I will discuss some recent work with Etienne Le Masson where we prove a "quantum ergodicity" result for eigenfunctions of the discrete Laplacian on large regular graphs. This means that, for most eigenfunctions $\psi_j$, the probability measure $|\psi_j(x)|^2$ on the vertices of the graph is close to uniform. I will also discuss possible extensions to other models.